/* ═══════════════════════════════════════════════════════════════
   Excel for Finance Notes — styles.css
   RequestNotes Design System — Dark Default + Light Mode
═══════════════════════════════════════════════════════════════ */

/* ── Reset ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 16px; scroll-behavior: smooth; }
body { font-family: 'Segoe UI', system-ui, -apple-system, sans-serif; line-height: 1.6; -webkit-font-smoothing: antialiased; }
a { color: inherit; text-decoration: none; }
img { max-width: 100%; display: block; }
button { font-family: inherit; cursor: pointer; border: none; background: none; }

/* ── Theme Tokens — Dark Default ── */
:root {
  --bg:            #09090b;
  --surface:       #111113;
  --card:          #18181b;
  --border:        #27272a;
  --border-light:  #3f3f46;
  --text:          #fafafa;
  --muted:         #a1a1aa;
  --dim:           #52525b;
  --accent:        #6366f1;
  --accent2:       #818cf8;
  --accent3:       #a5b4fc;
  --green:         #22c55e;
  --amber:         #f59e0b;
  --coral:         #f97316;
  --pink:          #ec4899;
  --teal:          #14b8a6;
  --shadow:        0 1px 3px rgba(0,0,0,0.4);
  --shadow-md:     0 4px 12px rgba(0,0,0,0.5);
  --radius:        6px;
  --radius-md:     8px;
  --radius-lg:     12px;
  --topbar-height: 40px;
}

/* ── Light Mode Overrides ── */
.light {
  --bg:          #fafaf9;
  --surface:     #f4f4f5;
  --card:        #ffffff;
  --border:      #e4e4e7;
  --border-light:#d4d4d8;
  --text:        #09090b;
  --muted:       #52525b;
  --dim:         #a1a1aa;
  --shadow:      0 1px 3px rgba(0,0,0,0.06);
  --shadow-md:   0 4px 12px rgba(0,0,0,0.08);
}
.light { --green-text: #15803d; --amber-text: #b45309; --coral-text: #c2410c; --pink-text: #be185d; --teal-text: #0f766e; }
body { background: var(--bg); color: var(--text); transition: background-color 0.2s ease, color 0.2s ease; }

/* ── Topbar ── */
.site-topbar {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  height: var(--topbar-height);
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center;
}
.topbar-inner { width: 100%; padding: 0 16px; display: flex; align-items: center; gap: 12px; }
.topbar-brand { display: flex; align-items: center; gap: 7px; font-size: 13px; font-weight: 600; color: var(--text); white-space: nowrap; flex-shrink: 0; }
.topbar-logo-mark { width: 22px; height: 22px; background: var(--accent); color: #fff; border-radius: 5px; display: flex; align-items: center; justify-content: center; font-size: 10px; font-weight: 700; }
.topbar-logo-text { color: var(--text); }
.topbar-breadcrumb { display: flex; align-items: center; gap: 5px; font-size: 12px; color: var(--muted); flex: 1; overflow: hidden; }
.topbar-bc-link { color: var(--muted); transition: color .15s ease; }
.topbar-bc-link:hover { color: var(--text); }
.topbar-bc-sep { color: var(--dim); }
.topbar-bc-current { color: var(--text); font-weight: 500; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.topbar-theme-toggle { margin-left: auto; width: 28px; height: 28px; display: flex; align-items: center; justify-content: center; color: var(--muted); border-radius: var(--radius); transition: all .15s ease; flex-shrink: 0; }
.topbar-theme-toggle:hover { color: var(--text); background: rgba(255,255,255,.05); }
.light .topbar-theme-toggle:hover { background: rgba(0,0,0,.05); }
.topbar-theme-toggle .icon-light { display: none; }
.topbar-theme-toggle .icon-dark  { display: inline; }
.light .topbar-theme-toggle .icon-dark  { display: none; }
.light .topbar-theme-toggle .icon-light { display: inline; }
.topbar-request { font-size: 11px; font-weight: 500; padding: 4px 10px; background: var(--accent); color: #fff; border-radius: var(--radius); white-space: nowrap; flex-shrink: 0; transition: opacity .15s ease; }
.topbar-request:hover { opacity: .85; }

/* ── App Layout ── */
.app-layout { display: flex; height: calc(100vh - var(--topbar-height)); margin-top: var(--topbar-height); overflow: hidden; }

/* ── Sidebar ── */
.sidebar { width: 240px; flex-shrink: 0; background: var(--surface); border-right: 1px solid var(--border); display: flex; flex-direction: column; overflow: hidden; height: calc(100vh - var(--topbar-height)); }
.sidebar-label { padding: 12px 14px 8px; font-size: 10px; font-weight: 600; text-transform: uppercase; letter-spacing: .07em; color: var(--dim); flex-shrink: 0; }
#toc-nav { flex: 1; overflow-y: auto; overflow-x: hidden; padding-bottom: 8px; }
#toc-nav::-webkit-scrollbar { width: 3px; }
#toc-nav::-webkit-scrollbar-thumb { background: var(--border-light); border-radius: 2px; }
#toc-nav::-webkit-scrollbar-track { background: transparent; }

/* TOC Items */
.toc-item { border-bottom: 1px solid var(--border); }
a.toc-header, a.toc-sub { text-decoration: none; color: inherit; display: flex; }
a.toc-header { align-items: center; gap: 8px; padding: 7px 14px; font-size: 13px; color: var(--muted); transition: all .15s ease; cursor: pointer; }
a.toc-header:hover { color: var(--text); background: rgba(255,255,255,.04); }
.light a.toc-header:hover { background: rgba(0,0,0,.04); }
a.toc-header.active { color: var(--accent); background: rgba(99,102,241,.07); border-left: 2px solid var(--accent); }
.toc-icon { font-size: 13px; flex-shrink: 0; }
.toc-label { flex: 1; }
.toc-chevron { font-size: 9px; color: var(--dim); transition: transform .2s ease; flex-shrink: 0; }
.toc-item.open .toc-chevron { transform: rotate(90deg); }
.toc-subs { display: none; }
.toc-item.open .toc-subs { display: block; }
a.toc-sub { display: block; padding: 5px 14px 5px 35px; font-size: 12px; color: var(--dim); transition: all .15s ease; }
a.toc-sub:hover { color: var(--muted); background: rgba(255,255,255,.02); }
.light a.toc-sub:hover { background: rgba(0,0,0,.02); }
a.toc-sub.active { color: var(--accent2); }

/* Progress */
.sidebar-footer { padding: 10px 14px; border-top: 1px solid var(--border); flex-shrink: 0; }
.progress-meta { display: flex; justify-content: space-between; font-size: 11px; color: var(--dim); margin-bottom: 5px; }
.progress-bar { height: 2px; background: var(--border); border-radius: 2px; overflow: hidden; }
.progress-fill { height: 100%; background: var(--accent); border-radius: 2px; width: 0%; transition: width .4s ease; }

/* ── Main Content ── */
.main-content { flex: 1; overflow-y: auto; height: calc(100vh - var(--topbar-height)); }
.main-content::-webkit-scrollbar { width: 6px; }
.main-content::-webkit-scrollbar-thumb { background: var(--border-light); border-radius: 3px; }
.main-content::-webkit-scrollbar-track { background: transparent; }

.main-header { padding: 16px 48px 0; max-width: 960px; margin: 0 auto; }
.breadcrumb { font-size: 12px; color: var(--dim); padding-bottom: 12px; border-bottom: 1px solid var(--border); margin-bottom: 4px; }
.breadcrumb .bc-active { color: var(--muted); }
#content-area { max-width: 960px; margin: 0 auto; padding: 0 48px 80px; }

/* ── Content Container ── */
.content-container { }
.content-container h2 { font-size: 19px; font-weight: 700; color: var(--text); margin: 22px 0 6px; line-height: 1.3; }
.content-container h3 { font-size: 16px; font-weight: 600; color: var(--text); margin: 18px 0 8px; line-height: 1.35; }
.content-container h4 { font-size: 12px; font-weight: 600; color: var(--muted); margin: 16px 0 6px; text-transform: uppercase; letter-spacing: .04em; }
.content-container p { color: var(--muted); font-size: 14.5px; line-height: 1.75; margin-bottom: 14px; }
.content-container ul, .content-container ol { color: var(--muted); font-size: 14.5px; line-height: 1.75; padding-left: 20px; margin-bottom: 14px; }
.content-container li { margin-bottom: 4px; }
.content-container strong { color: var(--text); font-weight: 600; }
.content-container em { color: var(--accent3); font-style: normal; font-weight: 500; }

/* ── Difficulty Badge ── */
.difficulty-badge { display: inline-flex; align-items: center; gap: 5px; padding: 3px 10px; border-radius: 20px; font-size: 11px; font-weight: 600; margin-bottom: 20px; border: 1px solid transparent; }
.difficulty-badge.beginner     { background: rgba(34,197,94,.1);  border-color: rgba(34,197,94,.25);  color: #22c55e; }
.difficulty-badge.intermediate { background: rgba(245,158,11,.1); border-color: rgba(245,158,11,.25); color: #f59e0b; }
.difficulty-badge.advanced     { background: rgba(249,115,22,.1); border-color: rgba(249,115,22,.25); color: #f97316; }
.difficulty-badge.expert       { background: rgba(239,68,68,.1);  border-color: rgba(239,68,68,.25);  color: #ef4444; }

/* ── Section Block ── */
.section-block { margin-bottom: 32px; }

/* ── Callout Boxes ── */
.callout { padding: 14px 18px; border-radius: var(--radius-md); border-left: 3px solid; margin: 20px 0; font-size: 14px; }
.callout p { margin-bottom: 0; font-size: 14px; }
.callout-info    { background: rgba(99,102,241,.07);  border-color: var(--accent);  color: var(--muted); }
.callout-warning { background: rgba(245,158,11,.07);  border-color: var(--amber);   color: var(--muted); }
.callout-success { background: rgba(34,197,94,.07);   border-color: var(--green);   color: var(--muted); }
.callout-danger  { background: rgba(249,115,22,.07);  border-color: var(--coral);   color: var(--muted); }
.callout-accent  { background: rgba(99,102,241,.08);  border-color: var(--accent2); color: var(--muted); }
.callout-teal    { background: rgba(20,184,166,.07);  border-color: var(--teal);    color: var(--muted); }
.callout strong  { color: var(--text); }

/* ── Formula Block ── */
.formula-block { background: var(--card); border: 1px solid var(--border); border-left: 3px solid var(--accent); border-radius: var(--radius-md); padding: 16px 20px; margin: 20px 0; }
.formula-label { font-size: 10px; text-transform: uppercase; letter-spacing: .07em; color: var(--dim); margin-bottom: 8px; font-weight: 600; }
.formula-body  { font-size: 16px; color: var(--text); font-style: italic; line-height: 1.6; }
.formula-vars  { margin-top: 12px; padding-top: 12px; border-top: 1px solid var(--border); }
.formula-vars p { font-size: 13px; color: var(--muted); margin-bottom: 4px; }
.formula-vars code { color: var(--accent3); background: rgba(99,102,241,.1); padding: 1px 5px; border-radius: 3px; font-size: 12px; }

/* ── Excel Formula Component — specialized for Excel functions ── */
.excel-formula { background: var(--card); border: 1px solid var(--border); border-top: 3px solid var(--accent); border-radius: var(--radius-md); margin: 20px 0; overflow: hidden; }
.ef-header { display: flex; align-items: center; justify-content: space-between; padding: 10px 16px; background: rgba(99,102,241,.06); border-bottom: 1px solid var(--border); }
.ef-name { font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace; font-size: 15px; font-weight: 700; color: var(--accent2); }
.ef-badge { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; padding: 2px 8px; border-radius: 20px; }
.ef-badge--lookup   { background: rgba(99,102,241,.15); color: var(--accent2); }
.ef-badge--finance  { background: rgba(245,158,11,.15); color: var(--amber); }
.ef-badge--logical  { background: rgba(20,184,166,.15); color: var(--teal); }
.ef-badge--math     { background: rgba(34,197,94,.15);  color: var(--green); }
.ef-badge--text     { background: rgba(236,72,153,.15); color: var(--pink); }
.ef-badge--date     { background: rgba(249,115,22,.15); color: var(--coral); }
.ef-badge--array    { background: rgba(99,102,241,.15); color: var(--accent2); }
.ef-syntax { padding: 12px 16px; border-bottom: 1px dashed var(--border); }
.ef-syntax code { font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace; font-size: 13.5px; color: var(--text); background: var(--surface); display: block; padding: 8px 12px; border-radius: var(--radius); line-height: 1.6; }
.ef-syntax code .ef-arg { color: var(--amber); }
.ef-syntax code .ef-opt-arg { color: var(--muted); }
.ef-body { padding: 12px 16px; }
.ef-desc { font-size: 14px; color: var(--muted); line-height: 1.7; margin-bottom: 10px; }
.ef-args { margin-bottom: 10px; }
.ef-args-title { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--dim); margin-bottom: 6px; }
.ef-arg-row { display: flex; gap: 10px; padding: 5px 0; border-bottom: 1px solid var(--border); font-size: 13px; }
.ef-arg-row:last-child { border-bottom: none; }
.ef-arg-name { font-family: 'Cascadia Code', Consolas, monospace; font-size: 12px; color: var(--amber); min-width: 120px; flex-shrink: 0; padding-top: 1px; }
.ef-arg-name.optional { color: var(--muted); }
.ef-arg-desc { color: var(--muted); line-height: 1.55; }
.ef-example { padding: 10px 16px 14px; background: rgba(99,102,241,.04); border-top: 1px solid var(--border); }
.ef-example-title { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--accent2); margin-bottom: 6px; }
.ef-example code { font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace; font-size: 13px; color: var(--green); display: block; margin-bottom: 4px; }
.ef-example p { font-size: 12.5px; color: var(--dim); margin: 0; line-height: 1.5; }

/* compact formula card */
.cs-formula-compact { border: 1px solid var(--border); border-top: 3px solid var(--accent); border-radius: var(--radius-md); overflow: hidden; margin: 0; background: var(--card); }
.cf-label   { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; color: var(--accent2); padding: 8px 12px 6px; background: rgba(99,102,241,.05); border-bottom: 1px solid var(--border); }
.cf-formula { font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace; font-size: 14px; font-weight: 600; color: var(--text); padding: 10px 12px 8px; line-height: 1.4; }
.cf-vars    { font-size: 11.5px; color: var(--muted); padding: 0 12px 8px; line-height: 1.55; border-top: 1px dashed var(--border); padding-top: 7px; }
.cf-example { font-size: 11.5px; color: var(--accent3); padding: 6px 12px 9px; background: rgba(99,102,241,.04); font-style: italic; border-top: 1px solid var(--border); line-height: 1.5; }

/* ── Keyboard Shortcut Badge ── */
.kbd-group { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.kbd-item { display: flex; align-items: center; gap: 8px; background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-md); padding: 8px 12px; }
.kbd-keys { display: flex; align-items: center; gap: 3px; flex-shrink: 0; }
kbd { display: inline-flex; align-items: center; justify-content: center; background: var(--surface); border: 1px solid var(--border-light); border-bottom: 2px solid var(--border-light); border-radius: 4px; padding: 2px 7px; font-family: 'Cascadia Code', Consolas, monospace; font-size: 11px; color: var(--text); white-space: nowrap; min-width: 24px; }
.kbd-desc { font-size: 13px; color: var(--muted); line-height: 1.4; }
.kbd-plus { font-size: 11px; color: var(--dim); }

/* ── Data Tables ── */
.table-wrapper { overflow-x: auto; margin: 20px 0; border-radius: var(--radius-md); border: 1px solid var(--border); }
table { width: 100%; border-collapse: collapse; font-size: 13.5px; }
thead { background: var(--card); }
th { padding: 10px 14px; text-align: left; color: var(--muted); font-weight: 600; font-size: 12px; text-transform: uppercase; letter-spacing: .04em; border-bottom: 1px solid var(--border); }
td { padding: 10px 14px; color: var(--muted); border-bottom: 1px solid var(--border); }
tr:last-child td { border-bottom: none; }
tr:hover td { background: rgba(255,255,255,.02); }
.light tr:hover td { background: rgba(0,0,0,.02); }
td strong { color: var(--text); }
.td-green  { color: var(--green)   !important; }
.td-coral  { color: var(--coral)   !important; }
.td-amber  { color: var(--amber)   !important; }
.td-accent { color: var(--accent2) !important; }
td code { font-family: 'Cascadia Code', Consolas, monospace; font-size: 12px; background: var(--surface); color: var(--accent3); padding: 1px 6px; border-radius: 3px; }

/* ── Code Blocks ── */
.code-block { background: #18181b; border: 1px solid #27272a; border-radius: var(--radius-md); margin: 20px 0; overflow: hidden; }
.light .code-block { background: #18181b; border-color: #27272a; }
.code-header { background: #111113; padding: 8px 14px; border-bottom: 1px solid #27272a; font-size: 11px; color: #71717a; font-weight: 600; }
.code-block code { display: block; padding: 14px 16px; font-family: 'Cascadia Code', 'Fira Code', 'Consolas', monospace; font-size: 13px; line-height: 1.7; color: #fafafa; white-space: pre; overflow-x: auto; }

/* ── Content Tabs ── */
.tabs-wrapper { margin: 20px 0; border: 1px solid var(--border); border-radius: var(--radius-md); overflow: hidden; }
.tabs-header { display: flex; background: var(--card); border-bottom: 1px solid var(--border); overflow-x: auto; }
.tab-btn { padding: 9px 18px; font-size: 13px; font-weight: 500; color: var(--muted); white-space: nowrap; border-bottom: 2px solid transparent; transition: all .15s ease; }
.tab-btn:hover { color: var(--text); }
.tab-btn.active { color: var(--accent); border-bottom-color: var(--accent); background: rgba(99,102,241,.05); }
.tab-panels { }
.tab-panel { display: none; padding: 20px; }
.tab-panel.active { display: block; }
.tab-panel p { color: var(--muted); font-size: 14px; line-height: 1.7; margin-bottom: 10px; }
.tab-panel p:last-child { margin-bottom: 0; }
.tab-panel ul { color: var(--muted); font-size: 14px; padding-left: 18px; line-height: 1.7; }

/* ── Expandable Blocks ── */
.expand-block { border: 1px solid var(--border); border-radius: var(--radius-md); margin: 16px 0; overflow: hidden; }
.expand-trigger { width: 100%; padding: 12px 16px; display: flex; justify-content: space-between; align-items: center; background: var(--card); font-size: 14px; color: var(--muted); text-align: left; cursor: pointer; transition: all .15s ease; }
.expand-trigger:hover { color: var(--text); }
.expand-trigger.open  { color: var(--text); }
.expand-arrow { font-size: 10px; transition: transform .2s ease; }
.expand-trigger.open .expand-arrow { transform: rotate(180deg); }
.expand-content { display: none; padding: 16px; border-top: 1px solid var(--border); }
.expand-content.open { display: block; }
.expand-content p { font-size: 14px; color: var(--muted); margin-bottom: 10px; }
.expand-content p:last-child { margin-bottom: 0; }

/* ── Quiz ── */
.quiz-question { margin-bottom: 24px; padding: 16px; background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-md); }
.quiz-q { font-size: 14px; color: var(--text); margin-bottom: 12px; font-weight: 500; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-opt { padding: 9px 14px; border: 1px solid var(--border); border-radius: var(--radius); font-size: 13.5px; color: var(--muted); text-align: left; background: var(--surface); cursor: pointer; transition: all .15s ease; }
.quiz-opt:hover { border-color: var(--accent); color: var(--text); }
.quiz-question.answered .quiz-opt { cursor: default; pointer-events: none; }
.quiz-opt.correct { background: rgba(34,197,94,.1);  border-color: var(--green); color: var(--green); }
.quiz-opt.wrong   { background: rgba(249,115,22,.1); border-color: var(--coral); color: var(--coral); }
.quiz-explain { display: none; margin-top: 12px; padding: 10px 14px; background: rgba(99,102,241,.07); border-radius: var(--radius); font-size: 13.5px; color: var(--muted); }
.quiz-question.answered .quiz-explain { display: block; }

/* ── Topic Quick Check ── */
.topic-quick-check { margin-top: 40px; padding-top: 32px; border-top: 1px solid var(--border); }
.topic-quick-check h3 { margin-bottom: 4px; }

/* ── Subtopic Mini Quiz ── */
.mini-quiz-section { margin-top: 40px; padding-top: 32px; border-top: 1px solid var(--border); }
.mini-quiz-section h3 { margin-bottom: 4px; }
.mini-quiz-block { margin-bottom: 32px; }
.mini-quiz-block h4, .knowledge-check-block h4 { font-size: 13px; text-transform: uppercase; letter-spacing: .05em; color: var(--muted); margin-bottom: 16px; }

/* ── Knowledge Check ── */
.kc-item { border: 1px solid var(--border); border-radius: var(--radius-md); margin-bottom: 10px; overflow: hidden; }
.kc-question { width: 100%; display: flex; justify-content: space-between; align-items: flex-start; padding: 12px 16px; background: var(--surface); border: none; cursor: pointer; text-align: left; gap: 12px; }
.kc-question:hover { background: rgba(99,102,241,.05); }
.light .kc-question:hover { background: rgba(99,102,241,.04); }
.kc-q-text { font-size: 14px; color: var(--text); font-weight: 500; line-height: 1.5; }
.kc-toggle { font-size: 11px; color: var(--muted); flex-shrink: 0; margin-top: 3px; transition: transform .2s ease; }
.kc-item.open .kc-toggle { transform: rotate(180deg); }
.kc-answer { display: none; padding: 14px 16px; border-top: 1px solid var(--border); background: var(--bg); font-size: 14px; line-height: 1.65; color: var(--muted); }
.kc-item.open .kc-answer { display: block; }
.kc-answer strong { color: var(--text); }
.kc-answer ul { padding-left: 18px; margin-top: 8px; }
.kc-answer li { margin-bottom: 5px; }
.kc-answer code { font-family: 'Cascadia Code', Consolas, monospace; font-size: 12px; background: var(--surface); color: var(--accent3); padding: 1px 5px; border-radius: 3px; }

/* ── Stat Cards ── */
.stat-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr)); gap: 12px; margin: 20px 0; }
.stat-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-md); padding: 16px; }
.stat-value { font-size: 22px; font-weight: 700; color: var(--sv-color, var(--accent2)); margin-bottom: 4px; }
.stat-label { font-size: 12px; color: var(--dim); }
.stat-sub   { font-size: 11px; color: var(--dim); margin-top: 2px; }

/* ── Compare Grid ── */
.compare-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin: 20px 0; }
.compare-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-md); padding: 18px; }
.compare-card h4 { font-size: 14px; font-weight: 600; color: var(--text); margin-bottom: 10px; text-transform: none; letter-spacing: 0; }
.compare-card ul { color: var(--muted); font-size: 13.5px; padding-left: 16px; }
.compare-card li { margin-bottom: 5px; }
.compare-card.pro-card { border-color: rgba(34,197,94,.2);  }
.compare-card.con-card { border-color: rgba(249,115,22,.2); }

/* ── Mental Model Box ── */
.mental-model { background: rgba(99,102,241,.05); border: 1px solid rgba(99,102,241,.2); border-radius: var(--radius-md); padding: 18px 20px; margin: 20px 0; }
.mental-model-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--accent2); margin-bottom: 8px; }
.mental-model p { color: var(--muted); font-size: 14px; margin-bottom: 0; }

/* ── Step List ── */
.step-list { list-style: none; padding: 0; margin: 16px 0; }
.step-list li, .step-list .step-item { display: flex; gap: 14px; align-items: flex-start; padding: 12px 0; border-bottom: 1px solid var(--border); }
.step-list li:last-child, .step-list .step-item:last-child { border-bottom: none; }
.step-num { width: 26px; height: 26px; flex-shrink: 0; background: var(--accent); color: #fff; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 12px; font-weight: 700; margin-top: 1px; }
.step-num.sn-green  { background: rgba(34,197,94,.15);  color: var(--green);   border: 1px solid rgba(34,197,94,.35); }
.step-num.sn-amber  { background: rgba(245,158,11,.15); color: var(--amber);   border: 1px solid rgba(245,158,11,.35); }
.step-num.sn-coral  { background: rgba(249,115,22,.15); color: var(--coral);   border: 1px solid rgba(249,115,22,.35); }
.step-num.sn-teal   { background: rgba(20,184,166,.15); color: var(--teal);    border: 1px solid rgba(20,184,166,.35); }
.step-num.sn-accent { background: rgba(99,102,241,.15); color: var(--accent2); border: 1px solid rgba(99,102,241,.35); }
.step-content { flex: 1; }
.step-content strong { display: block; color: var(--text); font-size: 14px; margin-bottom: 3px; }
.step-content span { color: var(--muted); font-size: 13.5px; line-height: 1.6; }

/* ── Misconception Callout ── */
.misconception { border: 1px solid rgba(249,115,22,.25); background: rgba(249,115,22,.05); border-radius: var(--radius-md); padding: 14px 18px; margin: 16px 0; }
.misconception-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--coral); margin-bottom: 6px; }
.misconception p { font-size: 14px; color: var(--muted); margin: 0; }

/* ── Do / Don't Block ── */
.do-dont-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 20px 0; }
.do-block, .dont-block { border-radius: var(--radius-md); padding: 16px; }
.do-block { background: rgba(34,197,94,.06); border: 1px solid rgba(34,197,94,.2); }
.dont-block { background: rgba(249,115,22,.06); border: 1px solid rgba(249,115,22,.2); }
.do-block .do-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--green); margin-bottom: 8px; }
.dont-block .dont-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--coral); margin-bottom: 8px; }
.do-block ul, .dont-block ul { list-style: none; padding: 0; margin: 0; }
.do-block li, .dont-block li { font-size: 13.5px; color: var(--muted); padding: 4px 0; border-bottom: 1px solid rgba(255,255,255,.05); }
.do-block li:last-child, .dont-block li:last-child { border-bottom: none; }
.do-block li::before { content: '✓ '; color: var(--green); font-weight: 700; }
.dont-block li::before { content: '✗ '; color: var(--coral); font-weight: 700; }

/* ── Subtopic Navigation ── */
.subtopic-nav { margin-top: 36px; padding: 14px 0 10px; border-top: 1px solid var(--border); }
.subtopic-nav-label { display: block; font-size: 11px; font-weight: 600; letter-spacing: .06em; text-transform: uppercase; color: var(--dim); margin-bottom: 8px; }
.subtopic-nav-links { display: flex; flex-wrap: wrap; gap: 6px; }
.subtopic-nav-link { display: inline-block; padding: 4px 10px; border-radius: 4px; font-size: 12px; color: var(--muted); background: var(--surface); border: 1px solid var(--border); text-decoration: none; transition: color .15s, border-color .15s; cursor: pointer; }
.subtopic-nav-link:hover { color: var(--text); border-color: var(--accent); }
.subtopic-nav-link.active { color: var(--accent); border-color: var(--accent); background: rgba(99,102,241,.07); font-weight: 500; pointer-events: none; }

/* ── Prev / Next Footer ── */
.topic-nav-footer { display: flex; justify-content: space-between; align-items: center; margin-top: 20px; padding-top: 16px; border-top: 1px solid var(--border); flex-wrap: wrap; gap: 8px; }
.topic-nav-prev, .topic-nav-next { font-size: 13px; color: var(--accent2); text-decoration: none; transition: color .15s; }
.topic-nav-prev:hover, .topic-nav-next:hover { color: var(--accent); }
.topic-nav-next { margin-left: auto; }

/* ── Cheatsheet ── */
.cheatsheet-section { margin-bottom: 36px; }
.cheatsheet-section:last-child { margin-bottom: 0; }
.cheatsheet-section > h3, .cs-section-title { font-size: 11px !important; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; color: var(--accent) !important; padding-left: 10px; border-left: 3px solid var(--accent); margin: 0 0 16px !important; line-height: 1.4; }
.cs-grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin: 12px 0; }
.cs-grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin: 12px 0; }
.cs-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-md); padding: 14px; }
.cs-card-title { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--accent2); margin-bottom: 8px; padding-bottom: 6px; border-bottom: 1px solid var(--border); }
.cs-card--green  .cs-card-title { color: var(--green);   }
.cs-card--amber  .cs-card-title { color: var(--amber);   }
.cs-card--coral  .cs-card-title { color: var(--coral);   }
.cs-card--teal   .cs-card-title { color: var(--teal);    }
.cs-card--accent .cs-card-title { color: var(--accent2); }
.cs-card--green  { border-color: rgba(34,197,94,.2);   }
.cs-card--amber  { border-color: rgba(245,158,11,.2);  }
.cs-card--coral  { border-color: rgba(249,115,22,.2);  }
.cs-card--teal   { border-color: rgba(20,184,166,.2);  }
.cs-card--accent { border-color: rgba(99,102,241,.25); }
.cs-items { display: flex; flex-direction: column; gap: 4px; }
.cs-items span { font-size: 12.5px; color: var(--muted); padding: 3px 0; border-bottom: 1px solid var(--border); }
.cs-items span:last-child { border-bottom: none; }
.cs-items strong { color: var(--text); }
.cs-formula-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin: 12px 0; }
.cs-formula-card { background: var(--card); border: 1px solid var(--border); border-top: 3px solid var(--accent); border-radius: var(--radius-md); padding: 12px; }
.cs-formula-card--green { border-top-color: var(--green) !important; }
.cs-formula-card--amber { border-top-color: var(--amber) !important; }
.cs-formula-card--coral { border-top-color: var(--coral) !important; }
.cs-formula-card--teal  { border-top-color: var(--teal)  !important; }
.cs-formula-label { font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--accent2); margin-bottom: 6px; }
.cs-formula-body  { font-family: 'Cascadia Code', 'Fira Code', Consolas, monospace; font-size: 12px; color: var(--text); background: var(--surface); border-radius: 4px; padding: 4px 8px; }
.cs-note { border-left: 3px solid var(--amber); background: rgba(245,158,11,.06); padding: 10px 14px; border-radius: var(--radius); font-size: 13px; color: var(--muted); margin: 12px 0 0; }
.cs-note strong { color: var(--amber); }
.cs-card-body { font-size: 13.5px; line-height: 1.75; color: var(--muted); }
.cs-card-body code { font-family: 'Cascadia Code', Consolas, monospace; font-size: 12px; background: var(--surface); color: var(--text); padding: 1px 5px; border-radius: 3px; }
.cs-highlight { display: block; font-family: 'Cascadia Code', Consolas, monospace; font-size: 12.5px; background: var(--surface); color: var(--text); border-radius: 5px; padding: 7px 11px; margin: 8px 0 4px; line-height: 1.55; white-space: pre-wrap; word-break: break-word; }
.cs-sub { font-size: 12px; color: var(--dim); margin-top: 3px; line-height: 1.5; }
.cs-tag { display: inline-block; font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: .05em; padding: 2px 7px; border-radius: 3px; margin: 2px 3px 2px 0; line-height: 1.6; }
.cs-tag--blue   { background: rgba(99,102,241,.12);  color: var(--accent2); }
.cs-tag--green  { background: rgba(34,197,94,.1);    color: var(--green);   }
.cs-tag--amber  { background: rgba(245,158,11,.1);   color: var(--amber);   }
.cs-tag--teal   { background: rgba(20,184,166,.1);   color: var(--teal);    }
.cs-tag--coral  { background: rgba(249,115,22,.1);   color: var(--coral);   }

/* ── Mobile Navigation ── */
.mobile-nav-toggle { display: none; }
.mobile-nav-icon { width: 18px; height: 18px; flex-shrink: 0; }
.sidebar-overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,.5); z-index: 149; }
.sidebar-overlay.open { display: block; }

@media (max-width: 767px) {
  /* overflow:visible so content taller than viewport can scroll naturally */
  .app-layout { display: block; overflow: visible; }
  .main-content { height: auto; overflow-y: visible; overflow-x: hidden; }
  #content-area { padding: 0 18px 80px; max-width: 100%; }
  .main-header { padding: 12px 18px 0; }

  /* Sidebar slides in from left */
  .sidebar {
    position: fixed; top: var(--topbar-height); left: 0; bottom: 0;
    width: 280px; height: calc(100vh - var(--topbar-height));
    z-index: 200; transform: translateX(-100%);
    transition: transform 0.28s cubic-bezier(0.4,0,0.2,1);
    box-shadow: 4px 0 24px rgba(0,0,0,0.4);
    overflow: hidden;
  }
  .sidebar.open { transform: translateX(0); }

  /* Mobile toggle — fixed top-right, flush to edge
     padding-left:6px nudges icon into the visible pill centre
     (button is 44px wide, right edge is hidden behind screen edge) */
  .mobile-nav-toggle {
    display: flex; align-items: center; justify-content: center;
    position: fixed; top: calc(var(--topbar-height) + 12px); right: 0; z-index: 198;
    width: 44px; height: 44px; padding: 0 0 0 6px;
    background: var(--surface); border: 1px solid var(--border);
    border-right: none; border-radius: 22px 0 0 22px;
    color: #6366f1; cursor: pointer;
    transition: background 0.15s, color 0.15s;
    box-shadow: -2px 2px 8px rgba(0,0,0,0.25);
  }
  .mobile-nav-toggle:hover { background: var(--card); color: #6366f1; outline: none; }
  .mobile-nav-toggle[aria-expanded="true"] { color: var(--accent); border-color: var(--accent); }
  .light .mobile-nav-toggle { box-shadow: -2px 2px 8px rgba(0,0,0,0.1); }

  /* Hide topbar breadcrumb on mobile — not enough space */
  .topbar-breadcrumb { display: none; }

  .topic-nav-footer { flex-direction: column; }
  .topic-nav-prev, .topic-nav-next { width: 100%; text-align: center; padding: 12px; border: 1px solid var(--border); border-radius: var(--radius-md); background: var(--card); }
  .topic-nav-next { margin-left: 0; }
  .stat-grid { grid-template-columns: 1fr 1fr; }
  .compare-grid, .do-dont-grid { grid-template-columns: 1fr; }
  .cs-grid-2, .cs-grid-3, .cs-formula-grid { grid-template-columns: 1fr; }
}