:root{font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:#21344a;background:#f3f7fb;font-size:16px;line-height:1.55}*{box-sizing:border-box}body{margin:0}button{font:inherit;cursor:pointer}button:focus-visible{outline:3px solid #e6a747;outline-offset:3px}.topbar{background:#132c49;color:#fff;min-height:82px;padding:14px clamp(18px,4vw,52px);display:flex;align-items:center;justify-content:space-between;gap:24px}.brand{display:flex;align-items:center;gap:13px}.brand img{width:48px;height:48px;object-fit:cover;border-radius:50%;border:2px solid #8ce4cd;background:#fff}.brand strong,.brand span{display:block}.brand strong{font-size:1.16rem;line-height:1.2}.brand span{color:#afc7d8;font-size:.86rem}.topbar p{color:#c4d6e3;margin:0;font-size:.92rem}.layout{max-width:1320px;margin:0 auto;display:grid;grid-template-columns:296px minmax(0,1fr);gap:26px;padding:28px clamp(18px,4vw,52px) 70px}.sidebar,.workspace{background:#fff;border:1px solid #dce7ef;border-radius:20px;box-shadow:0 12px 36px #23456a0b}.sidebar{padding:20px;align-self:start;position:sticky;top:20px;max-height:calc(100vh - 40px);display:flex;flex-direction:column}.sidebar-head{padding:4px 5px 14px}.eyebrow{color:#087e7b;font-weight:800;font-size:.79rem;letter-spacing:.1em;text-transform:uppercase}.sidebar h1{font-size:1.55rem;margin:3px 0 0}.level-switch{display:flex;background:#eaf0f5;padding:4px;border-radius:12px;margin-bottom:15px}.level-switch button{border:0;background:transparent;color:#405974;border-radius:9px;flex:1;padding:8px;font-weight:700}.level-switch button[aria-pressed=true]{background:#fff;color:#102f4e;box-shadow:0 2px 8px #16395d1e}#topics{overflow:auto;display:grid;gap:3px;padding-right:3px}#topics button{border:0;background:transparent;border-radius:11px;padding:11px 10px;text-align:left;color:#39526a;line-height:1.3;font-size:.91rem}#topics button:hover{background:#eff8f7}#topics button.active{background:#e0f3f0;color:#075e60;font-weight:750}#topics button span{display:block;color:#6d8395;font-size:.76rem;letter-spacing:.02em;margin-bottom:3px}.workspace{min-width:0;overflow:hidden}.topic-head{padding:33px clamp(24px,4vw,48px) 24px;background:linear-gradient(118deg,#ecf5fc 0%,#f5fafb 72%);border-bottom:1px solid #e1ecf2}.topic-head h2{font-size:clamp(1.8rem,3.5vw,2.65rem);line-height:1.16;letter-spacing:-.03em;margin:7px 0 10px;color:#152f4b}.topic-head p{margin:0;max-width:68ch;color:#486176}.mode-tabs{display:flex;gap:8px;padding:17px clamp(24px,4vw,48px) 0;border-bottom:1px solid #e3eaf0}.mode-tabs button{background:transparent;border:0;border-bottom:3px solid transparent;color:#516a7f;font-weight:750;padding:9px 14px 12px;white-space:nowrap}.mode-tabs button[aria-selected=true]{color:#087e7b;border-bottom-color:#0a9290}.study-panel{padding:26px clamp(24px,4vw,48px) 40px;max-width:840px}.study-panel[hidden]{display:none}.study-panel h3{color:#17334c;font-size:1.25rem;margin:0 0 11px}.study-panel p{margin:0 0 15px}.outcomes{background:#eaf7f4;border-left:4px solid #21a69b;border-radius:0 12px 12px 0;padding:19px 22px;margin:0 0 28px}.outcomes h3{font-size:1rem;margin-bottom:8px}.outcomes ul{margin:0;padding-left:20px}.outcomes li{margin:5px 0}.lesson-section{border-top:1px solid #e3eaf0;padding:22px 0 6px}.worked,.watchout{background:#f1f5fa;padding:18px 21px;border-radius:12px;margin:15px 0 24px}.worked strong,.watchout strong{color:#116f73}.watchout{background:#fff5e6}.watchout strong{color:#9b591c}.source-note{font-size:.86rem;color:#6a7c8d;border-top:1px solid #e4ebf1;padding-top:22px;margin-top:14px}.card-progress,.quiz-progress{font-size:.89rem;color:#647b8b;font-weight:700;margin-bottom:13px}.flashcard{width:100%;min-height:235px;background:#123d57;color:#fff;border:0;border-radius:20px;text-align:left;padding:28px 31px;box-shadow:0 11px 22px #153d5623;display:flex;flex-direction:column;justify-content:space-between;gap:20px}.flashcard.flipped{background:#126b70}.flashcard .side{font-size:.75rem;font-weight:800;letter-spacing:.16em;color:#addddc}.flashcard .card-text{font-size:clamp(1.3rem,2.8vw,1.8rem);font-weight:650;line-height:1.35}.flashcard .hint{font-size:.83rem;color:#c8e2e6}.card-actions,.quiz-actions{display:flex;align-items:center;gap:10px;margin-top:17px;flex-wrap:wrap}.secondary-btn,.primary-btn{border-radius:10px;padding:10px 17px;font-weight:700}.secondary-btn{background:#fff;border:1px solid #bed2dd;color:#244862}.primary-btn{background:#0b817e;border:1px solid #0b817e;color:white}.secondary-btn:disabled{opacity:.45;cursor:default}.quiz-question{font-size:1.3rem;font-weight:700;color:#183854;line-height:1.4;margin-bottom:18px}.choices{display:grid;gap:10px}.choice{display:block;text-align:left;width:100%;padding:13px 17px;border:1px solid #cddce6;border-radius:11px;background:#fff;color:#26445e}.choice:hover:not(:disabled){border-color:#0b8783;background:#f1faf8}.choice.correct{border-color:#1a9370;background:#def5e7;color:#11553d;font-weight:700}.choice.wrong{border-color:#d4665b;background:#fff0ec;color:#8a2f29}.choice:disabled{cursor:default}.feedback{margin-top:16px;padding:14px 17px;border-radius:10px;background:#eef6f7}.feedback strong{color:#0d6c68}.result{background:#e7f5f1;padding:25px;border-radius:16px}.result strong{font-size:1.7rem;color:#0e6a65}.empty{color:#6b7e8c}footer{max-width:1320px;margin:0 auto;padding:0 clamp(18px,4vw,52px) 40px;color:#667d90;font-size:.84rem}@media(max-width:840px){.topbar p{display:none}.layout{grid-template-columns:1fr;gap:15px;padding-top:16px}.sidebar{position:static;max-height:none}.sidebar-head{padding-bottom:8px}.sidebar h1{font-size:1.3rem}#topics{display:flex;overflow-x:auto;gap:5px;padding-bottom:3px}#topics button{flex:0 0 auto;max-width:190px;padding:10px 12px;background:#f3f7fa}.topic-head{padding-top:25px}.study-panel{padding-top:21px}}@media(max-width:480px){.topbar{padding:12px 17px}.layout{padding-left:12px;padding-right:12px}.sidebar{padding:15px}.mode-tabs{gap:0;justify-content:space-between}.mode-tabs button{padding-left:8px;padding-right:8px}.flashcard{min-height:210px;padding:24px}footer{padding-left:20px;padding-right:20px}}@media(prefers-reduced-motion:no-preference){.flashcard,.choice,.secondary-btn,.primary-btn{transition:background-color .15s ease,transform .15s ease}.flashcard:hover{transform:translateY(-2px)}}