:root{--color-page:#f6f7f9;--color-surface:#fff;--color-surface-soft:#f0f2f6;--color-text:#1b2232;--color-muted:#667085;--color-border:#e2e5eb;--color-primary:#2f6fed;--color-primary-dark:#1f55c7;--color-primary-soft:#e8f0fe;--color-success:#179557;--color-success-dark:#0f7443;--color-success-soft:#e6f6ed;--color-error:#d83c3c;--color-error-dark:#ae2b2b;--color-error-soft:#fdecec;--color-warning:#d98b06;--color-warning-soft:#fff5e0;--color-streak:#ff7a00;--color-heart:#ee3f62;--skill-vocabulary:#7c5cf0;--skill-listening:#0b9fd8;--skill-reading:#12a37a;--skill-speaking:#f2711c;--skill-writing:#db3f8c;--radius-small:8px;--radius:14px;--radius-large:20px;--shadow-card:0 1px 2px #1018280d, 0 1px 3px #1018280f;--shadow-raised:0 8px 24px #10182814;--font:"Be Vietnam Pro", system-ui, -apple-system, "Segoe UI", sans-serif;--font-reading:"Source Serif 4", Georgia, 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64px}.page--narrow{max-width:760px}.page-header{margin-bottom:24px}.page-header p{color:var(--color-muted);max-width:720px}.grid-2{grid-template-columns:repeat(2,minmax(0,1fr));gap:20px;display:grid}.grid-3{grid-template-columns:repeat(3,minmax(0,1fr));gap:20px;display:grid}.dashboard-grid{grid-template-columns:minmax(0,2fr) minmax(0,1fr);align-items:start;gap:20px;display:grid}.stack{flex-direction:column;gap:16px;display:flex}.row{flex-wrap:wrap;align-items:center;gap:12px;display:flex}.row--between{justify-content:space-between}@media (width<=900px){.nav-links a{padding:8px;font-size:.85rem}.dashboard-grid,.grid-3{grid-template-columns:1fr}}@media (width<=700px){.top-navigation__inner{gap:12px;padding:0 16px;overflow-x:auto}.page{padding:20px 16px 48px}.grid-2{grid-template-columns:1fr}}.button{letter-spacing:.01em;cursor:pointer;white-space:nowrap;border:1px solid #0000;border-radius:12px;justify-content:center;align-items:center;gap:8px;padding:11px 20px;font-size:.95rem;font-weight:700;transition:transform 60ms,box-shadow 60ms,background .15s;display:inline-flex;text-decoration:none!important}.button:active:not(:disabled){transform:translateY(2px);box-shadow:none!important}.button:disabled{cursor:not-allowed;opacity:.5}.button--primary{background:var(--color-primary);color:#fff;box-shadow:0 3px 0 var(--color-primary-dark)}.button--primary:hover:not(:disabled){background:color-mix(in srgb, var(--color-primary) 90%, #fff)}.button--success{background:var(--color-success);color:#fff;box-shadow:0 3px 0 var(--color-success-dark)}.button--danger{background:var(--color-error);color:#fff;box-shadow:0 3px 0 var(--color-error-dark)}.button--secondary{background:var(--color-surface);border-color:var(--color-border);color:var(--color-text);box-shadow:0 3px 0 var(--color-border)}.button--secondary:hover:not(:disabled){background:var(--color-surface-soft)}.button--ghost{color:var(--color-muted);background:0 0;padding:8px 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h3{margin-bottom:6px}.muted{color:var(--color-muted)}.small{font-size:.875rem}.badge{background:var(--color-surface-soft);color:var(--color-muted);border-radius:999px;align-items:center;gap:4px;padding:2px 10px;font-size:.78rem;font-weight:600;display:inline-flex}.badge--primary{background:var(--color-primary-soft);color:var(--color-primary)}.badge--success{background:var(--color-success-soft);color:var(--color-success)}.badge--error{background:var(--color-error-soft);color:var(--color-error)}.badge--warning{background:var(--color-warning-soft);color:var(--color-warning)}.progress-bar{background:var(--color-surface-soft);border-radius:999px;height:12px;overflow:hidden}.progress-bar__fill{background:var(--color-success);border-radius:999px;height:100%;transition:width 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160px}.lesson-body--wide{max-width:1080px}.exercise-instruction{margin-bottom:20px;font-size:1.45rem;font-weight:700}.exercise-prompt{margin-bottom:20px;font-size:1.15rem}.option-list{gap:12px;display:grid}.option-list--two-columns{grid-template-columns:repeat(2,minmax(0,1fr))}.option-button{text-align:left;border:2px solid var(--color-border);background:var(--color-surface);cursor:pointer;border-bottom-width:4px;border-radius:14px;align-items:center;gap:14px;width:100%;padding:14px 16px;font-size:1.02rem;transition:background .12s,border-color .12s;display:flex}.option-button:hover:not(:disabled){background:var(--color-surface-soft)}.option-button:disabled{cursor:default}.option-button__key{border:2px solid 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0;padding:0;list-style:none;display:grid}.example-list li{background:var(--color-surface-soft);border-radius:10px;padding:10px 14px}.example-list .example-en{font-weight:600}.example-list .example-vi{color:var(--color-muted);font-size:.92rem}.flashcard-grid{grid-template-columns:repeat(auto-fill,minmax(230px,1fr));gap:14px;display:grid}.word-card{border:1px solid var(--color-border);border-radius:var(--radius);background:var(--color-surface);padding:16px}.word-card__word{font-size:1.2rem;font-weight:700}.word-card__ipa{color:var(--color-muted);font-size:.9rem}.celebration{text-align:center;padding:48px 0}.celebration__emoji{margin-bottom:12px;font-size:4rem;animation:.5s pop}.ai-feedback{border:1px solid var(--color-border);border-radius:var(--radius);background:var(--color-surface);margin-top:16px;padding:18px 20px}.band-circle{background:var(--color-primary);color:#fff;border-radius:50%;flex:none;place-items:center;width:64px;height:64px;font-size:1.4rem;font-weight:800;display:grid}.criteria-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:10px;margin:14px 0;display:grid}.criteria-item{background:var(--color-surface-soft);border-radius:10px;padding:10px 12px;font-size:.9rem}.correction{border-bottom:1px solid var(--color-border);padding:10px 0;font-size:.93rem}.correction:last-child{border-bottom:none}.correction del{color:var(--color-error)}.correction ins{color:var(--color-success);font-weight:600;text-decoration:none}.mind-map{flex-direction:column;gap:0;display:flex;position:relative}.mind-map__start{grid-template-columns:repeat(4,1fr);gap:12px;margin-bottom:32px;display:grid}.mind-map__step{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius);align-items:center;gap:10px;padding:14px;font-size:.92rem;font-weight:600;display:flex}.mind-map__step-number{background:var(--color-primary);color:#fff;border-radius:50%;flex:none;place-items:center;width:30px;height:30px;font-weight:800;display:grid}.mind-map__level{grid-template-columns:240px 1fr;align-items:stretch;gap:0;display:grid;position:relative}.mind-map__spine{padding:12px 28px 12px 0;position:relative}.mind-map__spine:before{content:"";background:var(--color-border);width:3px;position:absolute;top:0;bottom:0;left:23px}.mind-map__level:first-of-type .mind-map__spine:before{top:40px}.mind-map__level:last-of-type .mind-map__spine:before{bottom:calc(100% - 40px)}.mind-map__node{align-items:flex-start;gap:14px;display:flex;position:relative}.mind-map__circle{z-index:1;background:var(--color-surface);border:3px solid var(--color-border);width:48px;height:48px;color:var(--color-muted);border-radius:50%;flex:none;place-items:center;font-weight:800;display:grid;position:relative}.mind-map__level.is-current .mind-map__circle{border-color:var(--color-primary);background:var(--color-primary);color:#fff;box-shadow:0 0 0 6px var(--color-primary-soft)}.mind-map__level.is-done .mind-map__circle{border-color:var(--color-success);background:var(--color-success);color:#fff}.mind-map__branches{grid-template-columns:repeat(5,minmax(0,1fr));gap:10px;padding:12px 0 28px;display:grid;position:relative}.mind-map__branches:before{content:"";background:var(--color-border);width:28px;height:3px;position:absolute;top:36px;left:-28px}.mind-map__branch{background:var(--color-surface);border:1px solid var(--color-border);border-top:4px solid var(--branch-color);border-radius:12px;padding:10px 12px;font-size:.85rem}.mind-map__branch strong{font-size:.92rem;display:block}.mind-map__level.is-locked .mind-map__branch{opacity:.55}@media (width<=900px){.mind-map__level{grid-template-columns:1fr}.mind-map__branches{grid-template-columns:repeat(2,1fr);padding-left:62px}.mind-map__branches:before{display:none}.mind-map__start{grid-template-columns:repeat(2,1fr)}}.skill-tabs{flex-wrap:wrap;gap:8px;margin-bottom:24px;display:flex}.skill-tab{border:2px solid var(--color-border);background:var(--color-surface);cursor:pointer;border-radius:12px;align-items:center;gap:8px;padding:10px 16px;font-weight:600;display:flex}.skill-tab.is-active{border-color:var(--tab-color);background:color-mix(in srgb, var(--tab-color) 10%, var(--color-surface));color:var(--tab-color)}.lesson-path{flex-direction:column;align-items:center;gap:18px;padding:20px 0;display:flex}.lesson-node{align-items:center;gap:18px;width:520px;max-width:100%;display:flex}.lesson-node:nth-child(4n+2){transform:translate(60px)}.lesson-node:nth-child(4n+4){transform:translate(-60px)}.lesson-node__circle{background:var(--node-color);color:#fff;cursor:pointer;width:72px;height:72px;box-shadow:0 6px 0 color-mix(in srgb, var(--node-color) 70%, #000);border:none;border-radius:50%;flex:none;place-items:center;font-size:1.6rem;display:grid}.lesson-node__circle:disabled{background:var(--color-border);cursor:not-allowed;box-shadow:0 6px #c9ced8}.lesson-node__circle.is-current{outline:6px solid color-mix(in srgb, var(--node-color) 25%, transparent)}.lesson-node__info{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius);flex:1;padding:12px 16px}.lesson-node__info h4{margin:0 0 2px}.stars{color:#f5b301;letter-spacing:2px}@media (width<=700px){.lesson-node:nth-child(n){transform:none}}.exam-shell{background:#fff;flex-direction:column;min-height:100vh;display:flex}.exam-header{color:#fff;background:#1b2232;justify-content:space-between;align-items:center;gap:16px;padding:10px 24px;font-size:.92rem;display:flex}.exam-timer{font-variant-numeric:tabular-nums;background:#ffffff1f;border-radius:8px;padding:4px 12px;font-size:1.05rem;font-weight:700}.exam-timer.is-urgent{background:var(--color-error)}.exam-subheader{border-bottom:1px solid var(--color-border);background:var(--color-surface-soft);padding:10px 24px;font-size:.92rem}.exam-split{flex:1;grid-template-columns:1fr 1fr;min-height:0;display:grid}.exam-split>*{max-height:calc(100vh - 170px);padding:24px 28px;overflow-y:auto}.exam-split>:first-child{border-right:6px solid var(--color-surface-soft)}.exam-single{flex:1;width:100%;max-width:900px;margin:0 auto;padding:24px 28px;overflow-y:auto}.exam-passage{font-family:var(--font-reading);white-space:pre-line;font-size:1.05rem;line-height:1.75}.exam-question{border-bottom:1px solid var(--color-border);padding:12px 0}.exam-question__number{border:2px solid var(--color-text);border-radius:6px;place-items:center;min-width:28px;height:28px;margin-right:10px;font-size:.85rem;font-weight:700;display:inline-grid}.exam-question label{cursor:pointer;align-items:flex-start;gap:8px;padding:4px 0;display:flex}.exam-navigator{border-top:1px solid var(--color-border);background:var(--color-surface);flex-wrap:wrap;align-items:center;gap:6px;padding:10px 24px;display:flex}.exam-navigator button{border:1px solid var(--color-border);cursor:pointer;background:#fff;border-radius:6px;min-width:34px;height:32px;font-size:.82rem}.exam-navigator button.is-answered{color:#fff;background:#1b2232;border-color:#1b2232}.result-question{border-bottom:1px solid var(--color-border);grid-template-columns:40px 1fr;gap:12px;padding:12px 0;display:grid}.result-mark{color:#fff;border-radius:50%;place-items:center;width:32px;height:32px;font-weight:800;display:grid}.result-mark.is-correct{background:var(--color-success)}.result-mark.is-wrong{background:var(--color-error)}.chart-box{border:1px solid var(--color-border);border-radius:var(--radius-small);background:#fff;padding:12px}@media (width<=900px){.exam-split{grid-template-columns:1fr}.exam-split>*{max-height:none}}.auth-page{background:radial-gradient(circle at 20% 10%, var(--color-primary-soft), transparent 50%), var(--color-page);place-items:center;min-height:100vh;padding:24px;display:grid}.auth-card{width:100%;max-width:420px}.spinner{border:3px solid var(--color-border);border-top-color:var(--color-primary);border-radius:50%;width:22px;height:22px;animation:.8s linear infinite spin;display:inline-block}.leaderboard-row{border-bottom:1px solid var(--color-border);grid-template-columns:48px 1fr auto;align-items:center;padding:14px 4px;display:grid}.leaderboard-row.is-me{background:var(--color-primary-soft);border-radius:10px}.rank{text-align:center;font-size:1.15rem;font-weight:800}.tab-switch{background:var(--color-surface-soft);border-radius:12px;gap:4px;padding:4px;display:inline-flex}.tab-switch button{cursor:pointer;color:var(--color-muted);background:0 0;border:none;border-radius:9px;padding:7px 14px;font-weight:600}.tab-switch button.is-active{background:var(--color-surface);color:var(--color-text);box-shadow:var(--shadow-card)}details>summary{cursor:pointer;font-weight:600}@keyframes spin{to{transform:rotate(360deg)}}@keyframes shake{25%{transform:translate(-5px)}75%{transform:translate(5px)}}@keyframes pulse{50%{opacity:.7}}@keyframes pop{0%{transform:scale(.4)}80%{transform:scale(1.15)}to{transform:scale(1)}}.lesson-node__circle.is-locked{background:var(--color-border);cursor:not-allowed;box-shadow:0 6px #c9ced8}