:root{--blue:#2563eb;--blue-dark:#1d4ed8;--green:#16a34a;--red:#dc2626;--yellow:#d97706;--bg:#f1f5f9;--card:#fff;--text:#1e293b;--muted:#64748b;--border:#cbd5e1}*{box-sizing:border-box;-webkit-tap-highlight-color:transparent}html{background:var(--bg);min-width:320px}body{background:var(--bg);min-height:100vh;color:var(--text);margin:0;font-family:-apple-system,BlinkMacSystemFont,HarmonyOS Sans SC,PingFang SC,Microsoft YaHei,sans-serif;font-size:17px}button,input{font:inherit}button,label,input{touch-action:manipulation}.app{width:min(100%,1120px);min-height:100vh;padding:max(18px, env(safe-area-inset-top)) max(18px, env(safe-area-inset-right)) max(28px, env(safe-area-inset-bottom)) max(18px, env(safe-area-inset-left));margin:0 auto}.app>div:not(.page-home)>h1,.app>div:not(.page-home)>.card,.app>div:not(.page-home)>.btn{width:min(100%,840px);margin-left:auto;margin-right:auto}.learning-nav{width:min(100%,840px);margin:0 auto 10px}.back-home{min-height:48px;color:var(--blue-dark);border:1px solid var(--border);cursor:pointer;background:0 0;border-radius:12px;padding:9px 14px;font-weight:700}.back-home:hover{background:#2563eb14}.back-home:active{transform:translateY(1px)}.card{background:var(--card);border:1px solid #94a3b838;border-radius:18px;margin-bottom:18px;padding:clamp(20px,3vw,30px);box-shadow:0 4px 18px #0f172a0f}h1{margin:8px 0 18px;font-size:clamp(26px,3vw,34px);line-height:1.25}p,li{line-height:1.65}.muted{color:var(--muted);font-size:15px}.page-heading{justify-content:space-between;align-items:center;gap:18px;margin-bottom:18px;display:flex}.page-heading h1{margin-bottom:0}.eyebrow{color:var(--blue);letter-spacing:.08em;margin:0 0 4px;font-size:14px;font-weight:700}.section-label{margin:12px 0;font-weight:700}.text-link{min-height:48px;color:var(--blue);border:1px solid var(--border);cursor:pointer;white-space:nowrap;background:0 0;border-radius:12px;padding:8px 14px}.home-grid{gap:18px;display:grid}.home-side{min-width:0}.task-list{margin:10px 0 20px;padding-left:26px}.task-list li{padding:3px 0 3px 5px}.privacy-note{color:var(--muted);font-size:14px;line-height:1.7}.button-row{grid-template-columns:repeat(2,minmax(0,1fr));gap:10px;display:grid}.status-message{color:var(--blue-dark);margin:14px 0 0;font-size:14px}.btn{color:#fff;background:var(--blue);cursor:pointer;border:0;border-radius:13px;width:100%;min-height:56px;margin-top:14px;padding:14px 18px;font-size:18px;font-weight:700;display:block}.btn:hover{background:var(--blue-dark)}.btn:active{transform:translateY(1px)}.btn.secondary{color:var(--text);background:#e2e8f0}.btn.secondary:hover{background:#cbd5e1}.button-row .btn{margin-top:8px;font-size:16px}.option{width:100%;min-height:56px;color:var(--text);text-align:left;cursor:pointer;background:#f8fafc;border:2px solid #dbe3ed;border-radius:13px;margin-bottom:12px;padding:15px 18px;font-size:17px;display:block}.option:hover{border-color:#93c5fd}.option.selected{border-color:var(--blue);background:#eff6ff}.option.correct{border-color:var(--green);background:#f0fdf4}.option.wrong{border-color:var(--red);background:#fef2f2}.input{width:100%;min-height:60px;color:var(--text);text-align:center;background:#fff;border:2px solid #dbe3ed;border-radius:13px;padding:14px 16px;font-size:20px}.input:focus{border-color:var(--blue);outline:3px solid #2563eb29}.hint,.explanation{border-radius:13px;margin-top:14px;padding:14px 16px;font-size:16px;line-height:1.65}.hint{color:#92400e;background:#fffbeb;border:1px solid #fde68a}.explanation{color:#1e3a8a;background:#eff6ff;border:1px solid #bfdbfe}.progress{color:var(--muted);margin:0 0 10px;font-size:15px;font-weight:600}.practice-card{min-height:360px}.question-pane,.answer-pane{min-width:0}.answer-pane{align-self:center}.stem{margin-bottom:18px;font-size:clamp(20px,2.4vw,26px);font-weight:700;line-height:1.55}.step-prompt{margin-bottom:16px;font-size:clamp(17px,2vw,21px);line-height:1.55}.sr-only{clip:rect(0, 0, 0, 0);white-space:nowrap;border:0;width:1px;height:1px;margin:-1px;padding:0;position:absolute;overflow:hidden}button:focus-visible,input:focus-visible{outline-offset:3px;outline:3px solid #2563eb52}@media (width>=760px){.app{padding:max(26px, env(safe-area-inset-top)) max(28px, env(safe-area-inset-right)) max(36px, env(safe-area-inset-bottom)) max(28px, env(safe-area-inset-left))}.card{border-radius:22px}}@media (width>=900px){.home-grid{grid-template-columns:minmax(0,1.35fr) minmax(300px,.65fr);align-items:start}.practice-card{grid-template-columns:minmax(0,1.1fr) minmax(320px,.9fr);align-items:center;gap:34px;padding:34px;display:grid}.answer-pane{border-left:1px solid #e2e8f0;padding-left:28px}}@media (width<=520px){.page-heading{flex-direction:column;align-items:flex-start}.text-link{width:100%}.button-row{grid-template-columns:1fr}}@media (prefers-reduced-motion:reduce){*,:before,:after{scroll-behavior:auto!important;transition:none!important}}