:root{--primary:#2563eb;--primary-soft:#eaf1ff;--bg:#f4f6fb;--surface:#ffffff;--text:#1a1f36;--text-muted:#5b6580;--border:#e6e9f2;--radius:16px;--radius-sm:10px;--shadow:0 8px 28px rgba(26,31,54,0.08);--shadow-sm:0 2px 10px rgba(26,31,54,0.06);--max:980px}*{box-sizing:border-box}body,html{margin:0;padding:0}body{background:var(--bg);color:var(--text);font-family:PingFang SC,Microsoft YaHei,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica,Arial,sans-serif;line-height:1.7;-webkit-font-smoothing:antialiased}a{color:var(--primary);text-decoration:none}a:hover{text-decoration:underline}.container{max-width:var(--max);margin:0 auto;padding:0 20px}.site-header{border-bottom:1px solid var(--border);background:rgba(255,255,255,.85);-webkit-backdrop-filter:saturate(180%) blur(8px);backdrop-filter:saturate(180%) blur(8px);position:sticky;top:0;z-index:10}.site-header .inner{display:flex;align-items:center;justify-content:space-between;padding:14px 20px;max-width:var(--max);margin:0 auto}.brand{font-weight:800;font-size:18px;color:var(--text)}.brand:hover{text-decoration:none}.brand .dot{color:var(--primary)}.nav a{color:var(--text-muted);font-weight:600;font-size:14px;margin-left:18px}.hero{padding:44px 0 12px}.hero h1{font-size:30px;margin:0 0 10px;letter-spacing:-.01em}.hero p{color:var(--text-muted);margin:0;font-size:16px}.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:18px;padding:24px 0 48px}.card{display:block;background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow-sm);padding:20px;transition:transform .15s ease,box-shadow .15s ease}.card:hover{text-decoration:none;transform:translateY(-2px);box-shadow:var(--shadow)}.card .top{display:flex;align-items:center;gap:10px;margin-bottom:6px}.card .icon{width:38px;height:38px;border-radius:10px;display:grid;place-items:center;font-size:20px}.card h3{margin:0;font-size:17px}.card .flagship-tag{font-size:11px;font-weight:700;color:var(--primary);background:var(--primary-soft);padding:2px 8px;border-radius:999px}.card .blurb{color:var(--text-muted);font-size:13px;margin:0 0 14px}.digest-peek{border-top:1px dashed var(--border);padding-top:12px}.digest-peek .date{font-size:12px;color:var(--text-muted);font-weight:600}.digest-peek .title{font-size:15px;font-weight:700;margin:4px 0;color:var(--text)}.digest-peek .summary{margin:0;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}.digest-peek .empty,.digest-peek .summary{font-size:13px;color:var(--text-muted)}.page-head{padding:36px 0 8px}.page-head .icon-big{width:52px;height:52px;border-radius:14px;display:grid;place-items:center;font-size:28px;margin-bottom:12px}.page-head h1{margin:0 0 8px;font-size:26px}.page-head p{margin:0;color:var(--text-muted)}.learn-cta{display:inline-block;margin-top:16px;background:var(--primary);color:#fff;font-weight:700;padding:10px 18px;border-radius:var(--radius-sm)}.learn-cta:hover{text-decoration:none;opacity:.92}.digest{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow-sm);padding:24px;margin:18px 0}.digest .meta{font-size:12px;color:var(--text-muted);font-weight:600;margin-bottom:6px}.digest h2{margin:0 0 12px;font-size:20px}.prose{font-size:15px;color:var(--text)}.prose h2{font-size:18px;margin:20px 0 8px}.prose h3{font-size:16px;margin:16px 0 6px}.prose p{margin:10px 0}.prose ol,.prose ul{padding-left:22px}.prose code{background:#f1f3f9;padding:1px 6px;border-radius:6px;font-size:13px}.sources{margin-top:16px;border-top:1px solid var(--border);padding-top:12px}.sources .label{font-size:12px;color:var(--text-muted);font-weight:700;margin-bottom:6px}.sources ul{margin:0;padding-left:18px}.sources li{font-size:13px;margin:3px 0}.empty-state{background:var(--surface);border:1px dashed var(--border);border-radius:var(--radius);padding:28px;margin:18px 0}.empty-state,.site-footer{text-align:center;color:var(--text-muted)}.site-footer{border-top:1px solid var(--border);font-size:13px;padding:28px 0}.back-link{display:inline-block;margin:20px 0 0;font-size:14px;font-weight:600}.lesson-meta{display:flex;align-items:center;justify-content:space-between;font-size:13px;color:var(--text-muted);font-weight:600;margin:8px 0 14px}.reset-btn{background:none;border:1px solid var(--border);color:var(--text-muted);border-radius:999px;padding:4px 12px;font-size:12px;cursor:pointer}.reset-btn:hover{background:#f1f3f9}.feedback{border-radius:var(--radius);padding:14px 18px;margin:0 0 16px;border:1px solid var(--border)}.feedback p{margin:6px 0 0;font-size:14px}.feedback-tag{font-size:12px;font-weight:800}.feedback-mastered{background:#ecfdf5;border-color:#a7f3d0}.feedback-mastered .feedback-tag{color:#059669}.feedback-partial{background:#fffbeb;border-color:#fde68a}.feedback-partial .feedback-tag{color:#d97706}.feedback-struggling{background:#eff6ff;border-color:#bfdbfe}.feedback-struggling .feedback-tag{color:#2563eb}.lesson{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow-sm);padding:24px}.lesson>h2{margin:0 0 16px;font-size:21px}.lesson-section{margin:18px 0;padding-top:14px;border-top:1px solid var(--border)}.lesson-section:first-of-type{border-top:none;padding-top:0}.lesson-label{font-size:13px;font-weight:800;color:var(--text-muted);margin-bottom:6px}.check{background:#f8fafc;margin:18px -24px -24px;padding:18px 24px 24px;border-radius:0 0 var(--radius) var(--radius)}.check-prompt{font-weight:600;margin:4px 0 10px}.check textarea{width:100%;border:1px solid var(--border);border-radius:var(--radius-sm);padding:12px;font-size:14px;font-family:inherit;resize:vertical;background:#fff}.check textarea:focus{outline:none;border-color:var(--primary)}.submit-btn{margin-top:12px;background:var(--primary);color:#fff;border:none;border-radius:var(--radius-sm);padding:11px 20px;font-size:14px;font-weight:700;cursor:pointer}.submit-btn:disabled{opacity:.5;cursor:not-allowed}.err{color:#dc2626;font-size:13px;margin-top:8px}