:root{--bg:#f2f3f5;--surface:#ffffff;--ink:#1c1f26;--ink-2:#5d6470;--line:#e3e5e8;--accent:#2f6fe4;--accent-ink:#ffffff;--accent-soft:#e9f0fd;--good:#1d7a4f;--warn:#b3541e;--bubble-user:#2f6fe4;--bubble-user-ink:#ffffff;--bubble-tutor:#ffffff;--radius:14px}@media (prefers-color-scheme:dark){:root{--bg:#0f1115;--surface:#191c22;--ink:#e8eaee;--ink-2:#9aa1ad;--line:#2a2e36;--accent:#5b8ff0;--accent-ink:#0f1115;--accent-soft:#1e2a42;--bubble-user:#3565c4;--bubble-user-ink:#f2f5fb;--bubble-tutor:#191c22}}*{box-sizing:border-box;margin:0;padding:0}body,html{height:100%}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;background:var(--bg);color:var(--ink);font-size:16px;line-height:1.45;-webkit-font-smoothing:antialiased}button{font:inherit;border:none;cursor:pointer;background:none;color:inherit}.app{max-width:640px;margin:0 auto;min-height:100dvh;display:flex;flex-direction:column}.screen{padding:20px 16px 32px;flex:1 1}.center{flex:1 1;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:12px;padding:24px;text-align:center;color:var(--ink-2)}.h1{font-size:22px;font-weight:700;letter-spacing:-.01em;color:var(--ink)}.sub{color:var(--ink-2);font-size:14px}.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius);padding:16px;width:100%;text-align:left;display:flex;flex-direction:column;gap:6px;transition:transform .16s cubic-bezier(.23,1,.32,1)}.card:active{transform:scale(.98)}.card-title{font-size:17px;font-weight:650}.badge{font-size:13px;color:var(--ink-2)}.badge.ok{color:var(--good)}.badge.warn{color:var(--warn)}.stack{display:flex;flex-direction:column;gap:10px}.btn{background:var(--accent);color:var(--accent-ink);border-radius:12px;padding:13px 18px;font-weight:600;font-size:16px;text-align:center;transition:transform .14s cubic-bezier(.23,1,.32,1),opacity .14s ease}.btn:active{transform:scale(.97)}.btn:disabled{opacity:.5;cursor:default}.btn-ghost{background:var(--accent-soft);color:var(--accent)}.grade-grid{display:grid;grid-template-columns:repeat(4,1fr);grid-gap:10px;gap:10px}.grade-btn{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:14px 0;font-size:17px;font-weight:600;transition:transform .14s cubic-bezier(.23,1,.32,1)}.grade-btn:active{transform:scale(.95)}.chat{display:flex;flex-direction:column;height:100dvh}.chat-head{display:flex;align-items:center;gap:10px;padding:12px 14px;background:var(--surface);border-bottom:1px solid var(--line);position:-webkit-sticky;position:sticky;top:0;z-index:5}.chat-head .title{font-weight:650;font-size:16px;flex:1 1}.chat-head .meta{font-size:12px;color:var(--ink-2)}.icon-btn{padding:8px 10px;border-radius:10px;color:var(--accent);font-weight:600;font-size:14px}.msgs{flex:1 1;overflow-y:auto;padding:16px 14px;display:flex;flex-direction:column;gap:10px}.msg{max-width:86%;padding:10px 14px;border-radius:16px;white-space:pre-wrap;word-break:break-word;font-size:15.5px}.msg.user{align-self:flex-end;background:var(--bubble-user);color:var(--bubble-user-ink);border-bottom-right-radius:6px}.msg.tutor{background:var(--bubble-tutor);border:1px solid var(--line);border-bottom-left-radius:6px}.msg.tutor,.typing{align-self:flex-start}.typing{color:var(--ink-2);font-size:14px;padding:4px 8px}.composer{display:flex;gap:8px;padding:10px 12px calc(10px + env(safe-area-inset-bottom));background:var(--surface);border-top:1px solid var(--line);position:-webkit-sticky;position:sticky;bottom:0}.composer textarea{flex:1 1;resize:none;border:1px solid var(--line);border-radius:12px;padding:11px 13px;font:inherit;font-size:15.5px;background:var(--bg);color:var(--ink);max-height:120px}.composer textarea:focus{outline:2px solid var(--accent);outline-offset:-1px}.send{background:var(--accent);color:var(--accent-ink);border-radius:12px;padding:0 16px;font-weight:650;transition:transform .14s cubic-bezier(.23,1,.32,1),opacity .14s ease}.send:active{transform:scale(.95)}.send:disabled{opacity:.45}.disclaimer{text-align:center;font-size:11.5px;color:var(--ink-2);padding:4px 12px 8px;background:var(--surface)}.notice{background:var(--accent-soft);color:var(--ink);border-radius:var(--radius);padding:14px;font-size:14px}@media (prefers-reduced-motion:reduce){.btn,.card,.grade-btn,.send{transition:none}}