/* 24点 —— 样式 */
:root{
  --bg:#0f172a;--panel:#1e293b;--text:#f1f5f9;--muted:#94a3b8;--accent:#7c3aed;
  --num-bg:#ffffff;--key-bg:#334155;--ok:#22c55e;--err:#ef4444;
}
*{box-sizing:border-box}html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--text);font-family:system-ui,-apple-system,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Noto Sans SC",sans-serif;line-height:1.5}
a{color:var(--accent);text-decoration:underline;text-decoration-thickness:2px;text-underline-offset:3px}
a:focus-visible{outline:3px solid var(--accent);outline-offset:3px}
.skip-link{position:absolute;left:-9999px;top:auto;width:1px;height:1px;overflow:hidden}
.skip-link:focus{position:static;width:auto;height:auto;padding:1rem;background:#000;color:#fff}
.site-header{background:var(--panel);border-bottom:1px solid #334155;padding:0.75rem 0}
.header-inner{max-width:1000px;margin:0 auto;padding:0 1rem;display:flex;align-items:center;gap:1rem;flex-wrap:wrap}
.brand{color:var(--text);text-decoration:none;font-weight:800;font-size:1.25rem;letter-spacing:0.05em}
.main-nav{margin-left:auto}
.nav-list{display:flex;gap:0.75rem;list-style:none;margin:0;padding:0}
.nav-link{color:var(--muted);text-decoration:none;padding:0.4rem 0.75rem;border-radius:6px}
.nav-link:hover,.nav-link:focus-visible{background:#334155;color:var(--text)}
.container{max-width:1000px;margin:0 auto;padding:0 1rem}
.hero{padding:2.5rem 0;background:linear-gradient(180deg,#0f172a,#0b1021)}
.hero-grid{display:flex;flex-direction:column;gap:2rem;align-items:center;text-align:center}
@media(min-width:768px){.hero-grid{flex-direction:row;text-align:left;align-items:center}}
.eyebrow{color:var(--accent);font-size:0.9rem;text-transform:uppercase;letter-spacing:0.1em;margin:0 0 0.5rem;display:flex;align-items:center;justify-content:center;gap:0.5rem}
@media(min-width:768px){.eyebrow{justify-content:flex-start}}
.hero h1{font-size:clamp(2rem,5vw,3rem);margin:0 0 1rem;line-height:1.1}
.hero-lede{color:var(--muted);font-size:1.05rem;max-width:62ch;margin:0 0 1.5rem}
.hero-actions{display:flex;gap:0.75rem;flex-wrap:wrap;justify-content:center}
@media(min-width:768px){.hero-actions{justify-content:flex-start}}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:0.4rem;padding:0.6rem 1.2rem;border:1px solid transparent;border-radius:8px;font-weight:700;font-size:1rem;cursor:pointer;text-decoration:none;transition:transform .1s,background .2s}
.btn:active{transform:scale(0.97)}
.btn:focus-visible{outline:3px solid var(--accent);outline-offset:3px}
.btn-primary{background:var(--accent);color:#fff;border-color:var(--accent)}
.btn-primary:hover{background:#a855f7}
.btn-secondary{background:transparent;color:var(--text);border:1px solid #475569}
.btn-secondary:hover{background:#334155}
.btn-outline{background:transparent;color:var(--text);border:1px solid #475569;padding:0.45rem 1rem;font-size:0.95rem}
.btn-outline:hover{background:#334155}
.section{padding:2rem 0}
.game-header{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:0.75rem;margin-bottom:1.25rem}
.game-header h2{margin:0;font-size:1.5rem}
.game-controls{display:flex;gap:0.5rem;flex-wrap:wrap;align-items:center}
.stat-wrap{display:flex;align-items:center;gap:0.4rem;font-size:0.95rem;color:var(--muted)}
.stat-wrap span:last-child{color:var(--text);font-variant-numeric:tabular-nums;font-weight:800}
.game24-wrap{display:flex;flex-direction:column;align-items:center;gap:1rem;margin:1rem 0}
.numbers{display:flex;gap:0.75rem;flex-wrap:wrap;justify-content:center}
.num{width:64px;height:64px;border-radius:12px;background:var(--num-bg);color:#000;display:flex;align-items:center;justify-content:center;font-weight:900;font-size:1.75rem;box-shadow:0 4px 12px rgba(0,0,0,0.25)}
.expression{min-height:48px;padding:0.75rem 1rem;border:2px dashed #334155;border-radius:10px;background:#0b1021;color:var(--text);font-variant-numeric:tabular-nums;font-size:1.25rem;text-align:center;min-width:260px;word-break:break-all}
.ops{display:flex;flex-wrap:wrap;gap:0.5rem;justify-content:center;max-width:520px;margin:0 auto}
.op-btn{width:48px;height:44px;border-radius:8px;border:1px solid #475569;background:var(--key-bg);color:var(--text);font-size:1.1rem;font-weight:700;cursor:pointer}
.op-btn:focus-visible{outline:3px solid var(--accent);outline-offset:2px}
.op-btn:hover{background:#475569}
.op-btn.clear{background:#334155;color:#f1f5f9}
.op-btn.submit{background:var(--accent);color:#fff;border-color:var(--accent)}
.op-btn.submit:hover{background:#a855f7}
.expr-input{width:min(100%,420px);padding:0.5rem 0.75rem;border:1px solid #475569;border-radius:8px;background:var(--key-bg);color:var(--text);text-align:center;font-size:1rem;margin-top:0.5rem}
.expr-input:focus-visible{outline:3px solid var(--accent);outline-offset:2px}
.game-status{margin-top:1rem;padding:0.75rem 1rem;background:var(--panel);border-radius:8px;border:1px solid #334155;font-size:0.95rem;color:var(--muted)}
#message{margin-top:0.5rem;min-height:1.3rem;color:var(--accent);font-weight:700}
#how-to-play{margin-top:1.5rem}
#how-to-play h3{margin-top:0;font-size:1.1rem;color:var(--accent)}
#how-to-play ul{color:var(--muted);padding-left:1.2rem}
#how-to-play li{margin:0.35rem 0}
.preview-num{width:56px;height:56px;border-radius:10px;background:#ffffff;color:#000;display:flex;align-items:center;justify-content:center;font-weight:900;font-size:2rem;margin:0.5rem 0;box-shadow:0 0 16px rgba(255,255,255,0.3)}
.site-footer{margin-top:3rem;padding:1.5rem 0;border-top:1px solid #334155;color:var(--muted);font-size:0.9rem;text-align:center}
.site-footer a{color:var(--accent)}
@media(prefers-reduced-motion: reduce){*{animation:none!important;transition:none!important;scroll-behavior:auto!important}}