:root {
  --bg:#f7f6f2; --surface:#fff; --ink:#18211d; --muted:#64706a;
  --green:#245c45; --green2:#3f8164; --soft:#e8efe9; --line:#e4e7e3;
  --gold:#ad7d23; --danger:#9b3d36; --shadow:0 10px 35px rgba(24,33,29,.07);
}
*{box-sizing:border-box} html{scroll-behavior:smooth} body{margin:0;background:var(--bg);color:var(--ink);font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;line-height:1.55}
button{font:inherit}.topbar{position:sticky;top:0;z-index:20;background:rgba(247,246,242,.93);backdrop-filter:blur(12px);border-bottom:1px solid var(--line);min-height:76px;display:flex;align-items:center;justify-content:space-between;padding:0 max(24px,calc((100vw - 1160px)/2))}
.brand{display:flex;align-items:center;gap:11px;text-decoration:none;color:var(--ink)}.brand-mark{width:42px;height:42px;border-radius:13px;display:grid;place-items:center;background:var(--green);color:white;font-size:23px}.brand strong,.brand small{display:block}.brand small{color:var(--muted);font-size:12px}
nav{display:flex;gap:6px}.nav-link{border:0;background:transparent;padding:10px 14px;border-radius:10px;color:var(--muted);cursor:pointer}.nav-link.active,.nav-link:hover{background:var(--soft);color:var(--green)}
main{width:min(1160px,calc(100% - 32px));margin:34px auto 70px}.hero{display:grid;grid-template-columns:1.45fr .8fr;gap:24px;margin-bottom:34px}.hero-main,.card{background:var(--surface);border:1px solid var(--line);box-shadow:var(--shadow);border-radius:22px}.hero-main{padding:36px}.eyebrow{color:var(--green2);font-weight:750;font-size:13px;text-transform:uppercase;letter-spacing:.08em}.hero h1{font-size:clamp(35px,5vw,58px);line-height:1.02;margin:8px 0 16px;letter-spacing:-.04em}.hero p{color:var(--muted);font-size:17px;max-width:700px}.hero-side{padding:28px;display:flex;flex-direction:column;justify-content:center}.score-big{font-size:44px;font-weight:800;letter-spacing:-.04em}.muted{color:var(--muted)}
.progress{height:10px;background:#edf0ed;border-radius:999px;overflow:hidden}.progress>span{display:block;height:100%;background:var(--green2);border-radius:999px}.stats{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-top:18px}.stat{padding:13px;border-radius:14px;background:var(--soft)}.stat strong{display:block;font-size:20px}.stat span{font-size:12px;color:var(--muted)}
.section-head{display:flex;justify-content:space-between;align-items:end;gap:20px;margin:34px 0 16px}.section-head h2{font-size:27px;margin:0}.section-head p{margin:0;color:var(--muted)}
.ladder{display:grid;gap:14px}.level{background:var(--surface);border:1px solid var(--line);border-radius:18px;padding:22px;display:grid;grid-template-columns:64px 1fr auto;gap:18px;align-items:center}.level.locked{opacity:.62}.level-number{width:56px;height:56px;border-radius:16px;background:var(--soft);color:var(--green);display:grid;place-items:center;font-size:22px;font-weight:800}.level.done .level-number{background:var(--green);color:white}.level h3{margin:0 0 4px}.level p{margin:0;color:var(--muted);font-size:14px}.level-meta{display:flex;gap:8px;margin-top:9px;flex-wrap:wrap}.pill{background:#f1f3f1;border-radius:999px;padding:5px 9px;font-size:12px;color:var(--muted)}
.btn{border:0;border-radius:12px;padding:11px 16px;font-weight:700;cursor:pointer}.btn-primary{background:var(--green);color:white}.btn-secondary{background:var(--soft);color:var(--green)}.btn-ghost{background:#f3f4f3;color:var(--ink)}.btn:disabled{opacity:.45;cursor:not-allowed}
.grid-2{display:grid;grid-template-columns:1fr 1fr;gap:18px}.card{padding:24px}.card h2,.card h3{margin-top:0}.chapter-list{display:grid;gap:12px}.chapter-item{padding:18px;border:1px solid var(--line);border-radius:16px;background:white;display:flex;justify-content:space-between;gap:14px;align-items:center}.chapter-item.locked{opacity:.55}.chapter-title strong{display:block}.chapter-title span{font-size:13px;color:var(--muted)}
.lesson-shell{display:grid;grid-template-columns:245px 1fr;gap:20px}.lesson-nav{position:sticky;top:96px;align-self:start}.lesson-nav .card{padding:16px}.lesson-nav button{width:100%;text-align:left;border:0;border-radius:10px;padding:10px;background:transparent;cursor:pointer;color:var(--muted)}.lesson-nav button.active{background:var(--soft);color:var(--green);font-weight:700}.lesson-content{min-width:0}.lesson-hero{padding:30px}.lesson-hero h1{margin:4px 0 10px;font-size:38px}.lesson-hero p{color:var(--muted)}
.explain{padding:24px;margin-top:16px}.explain h3{margin-bottom:8px}.math-box{background:#f4f6f4;border-left:4px solid var(--green2);padding:16px 18px;border-radius:10px;margin:13px 0;font-size:18px}.tip{background:#fff8e9;border:1px solid #efdfb8;padding:14px 16px;border-radius:12px;margin:14px 0}.exercise{margin-top:16px;padding:24px}.exercise-head{display:flex;justify-content:space-between;gap:15px;align-items:flex-start}.qnum{color:var(--green2);font-size:12px;font-weight:800;text-transform:uppercase;letter-spacing:.08em}.question{font-size:20px;font-weight:700;margin:8px 0 16px}.answers{display:grid;gap:9px}.answer{border:1px solid var(--line);background:white;text-align:left;padding:13px 15px;border-radius:12px;cursor:pointer}.answer:hover{border-color:#acc3b4}.answer.selected{border-color:var(--green2);background:var(--soft)}.answer.correct{border-color:#4b8a67;background:#ebf7ef}.answer.wrong{border-color:#b8665f;background:#fff0ee}.feedback{margin-top:14px;padding:14px;border-radius:12px;background:#f4f6f4}.feedback.correct{background:#ebf7ef}.feedback.wrong{background:#fff0ee}.lesson-actions{display:flex;justify-content:space-between;gap:12px;margin-top:18px}
.practice-hero{display:grid;grid-template-columns:1.3fr .7fr;gap:18px}.test-options{display:grid;gap:10px;margin-top:18px}.test-option{display:flex;justify-content:space-between;align-items:center;border:1px solid var(--line);padding:14px;border-radius:13px}.test-shell{max-width:840px;margin:auto}.test-top{display:flex;justify-content:space-between;align-items:center;margin-bottom:14px}.timer{font-variant-numeric:tabular-nums;font-weight:800}.result{padding:30px;text-align:center}.result-score{font-size:62px;font-weight:850;color:var(--green)}.review-tags{display:flex;flex-wrap:wrap;gap:8px}.review-tag{border:1px solid var(--line);background:white;padding:8px 11px;border-radius:999px;cursor:pointer}.review-tag.active{background:var(--green);color:white;border-color:var(--green)}
.empty{padding:34px;text-align:center;color:var(--muted)}
footer{width:min(1160px,calc(100% - 32px));margin:0 auto 45px;padding-top:24px;border-top:1px solid var(--line);font-size:13px;color:var(--muted)}footer a{color:var(--green)}
@media(max-width:820px){.topbar{padding:0 16px}.brand small{display:none}.nav-link{padding:9px 10px;font-size:13px}.hero,.practice-hero,.grid-2,.lesson-shell{grid-template-columns:1fr}.lesson-nav{position:static}.lesson-nav .card{display:flex;overflow:auto;gap:5px}.lesson-nav button{width:auto;white-space:nowrap}.level{grid-template-columns:52px 1fr}.level>.btn{grid-column:1/-1}.stats{grid-template-columns:1fr 1fr 1fr}.hero-main{padding:26px}.hero-side{padding:22px}}
@media(max-width:520px){main{width:min(100% - 20px,1160px);margin-top:20px}.topbar{min-height:66px}.brand span:nth-child(2){display:none}.hero h1{font-size:38px}.level{padding:17px}.stats{grid-template-columns:1fr}.section-head{align-items:start;flex-direction:column}.card{padding:19px}.lesson-hero h1{font-size:31px}}

.save-actions{display:flex;flex-wrap:wrap;gap:10px;margin:20px 0 14px}.file-button{display:inline-flex;align-items:center;justify-content:center}.save-message{margin-top:14px;padding:13px 15px;border-radius:12px;font-weight:650}.save-message.success{background:#ebf7ef;color:#245c45}.save-message.error{background:#fff0ee;color:var(--danger)}.backup-stats{display:grid;grid-template-columns:1fr;gap:9px;margin-top:18px}.backup-stats>div{padding:12px 14px;border-radius:13px;background:var(--soft)}.backup-stats strong,.backup-stats span{display:block}.backup-stats strong{font-size:19px}.backup-stats span{font-size:12px;color:var(--muted)}.danger-zone{margin-top:18px}.danger-btn{border:1px solid #e3c4c1;color:var(--danger);background:#fff8f7}
@media(max-width:700px){.topbar{align-items:flex-start;gap:8px;padding-top:10px;padding-bottom:10px}.topbar nav{overflow-x:auto;max-width:72vw}.nav-link{white-space:nowrap}.save-actions>.btn,.save-actions>.file-button{width:100%}}