@font-face{font-family:"DejaVu Sans";src:url(/assets/fonts/dejavu-sans.woff2) format("woff2");font-weight:400;font-display:swap}@font-face{font-family:"DejaVu Sans";src:url(/assets/fonts/dejavu-sans-bold.woff2) format("woff2");font-weight:600 800;font-display:swap}/* ==========================================================================
   Perimeter Playground — shared style
   Adapted from michaelleung.info/games (dark teal + light blue)
   ========================================================================== */
:root {
  --teal-darkest:#1a2332; --teal-dark:#233046; --teal-mid:#2b6f6f;
  --accent:#2a8080; --accent-soft:#a8dadc; --accent-tint:#eaf5f8;
  --ink:#17262e; --ink-soft:#4c636d; --line:#dde9ec;
  --paper:#fff; --cream:#f7f4ee; --radius:18px;
  --shadow:0 10px 30px rgba(18, 60, 60, 0.10);
  --shadow-hover:0 18px 44px rgba(18, 60, 60, 0.18);
}
* { margin:0; padding:0; box-sizing:border-box; }
html { scroll-behavior:smooth; }
body {
  font-family:"DejaVu Sans",Verdana,"Segoe UI", "Helvetica Neue", Arial, "Noto Sans", "Microsoft JhengHei", "PingFang TC", sans-serif;
  color:var(--ink); background:var(--paper); line-height:1.65;
  -webkit-font-smoothing:antialiased;
}
img, svg { max-width:100%; }
a { color:var(--teal-mid); text-decoration:none; }
a:hover { color:var(--teal-dark); }
.container { width:min(1180px, 92%); margin:0 auto; }
.sr-only { position:absolute; width:1px; height:1px; overflow:hidden; clip:rect(0 0 0 0); white-space:nowrap; }
[hidden] { display:none !important; } /* .overlay/.challenge-list set display:grid — author rules beat the UA [hidden] rule without this */

/* skip link + header */
.skip-link { position:absolute; left:-9999px; top:0; background:var(--accent); color:var(--teal-darkest); padding:.6rem 1rem; border-radius:0 0 10px 0; z-index:200; }
.skip-link:focus { left:0; }
.site-header { position:sticky; top:0; z-index:100; background:var(--teal-darkest); border-bottom:1px solid rgba(42, 128, 128, 0.18); }
.nav { display:flex; align-items:center; justify-content:space-between; padding:.9rem 0; gap:1rem; }
.brand { display:flex; align-items:center; gap:.6rem; color:#fff; font-weight:700; font-size:1.1rem; }
.brand:hover { color:var(--accent-soft); }
.brand-logo { height:34px; width:34px; }
.brand .brand-name { color:var(--accent); }
.brand:hover .brand-name { color:var(--accent-soft); }
.nav-links { display:flex; align-items:center; gap:.4rem; list-style:none; }
.nav-links a { color:#dcebee; font-size:.95rem; padding:.45rem .9rem; border-radius:999px; transition:background .2s, color .2s; }
.nav-links a:hover { background:rgba(42, 128, 128, 0.15); color:#fff; }
.nav-links a.active { background:var(--accent); color:var(--teal-darkest); font-weight:600; }
.lang-btn { background:rgba(42,128,128,.16); color:var(--accent-soft); border:1px solid rgba(42,128,128,.45); border-radius:999px; padding:.45rem .9rem; font:inherit; font-size:.9rem; font-weight:600; cursor:pointer; }
.lang-btn:hover { background:rgba(42,128,128,.3); color:#fff; }
.nav-toggle { display:none; background:none; border:1px solid rgba(42,128,128,.4); color:#fff; border-radius:10px; padding:.4rem .7rem; font-size:1.1rem; cursor:pointer; }

/* hero */
.hero { position:relative; overflow:hidden; color:#fff;
  background:radial-gradient(1100px 500px at 50% -10%, rgba(42,128,128,.22), transparent 60%),
              linear-gradient(160deg, var(--teal-darkest) 0%, var(--teal-dark) 55%, #22605f 100%);
  text-align:center; padding:5rem 0 4.2rem; }
#hero-particles { position:absolute; top:0; left:0; width:100%; height:100%; pointer-events:none; }
.hero-inner { position:relative; z-index:2; }
.pill { display:inline-block; padding:.4rem 1.1rem; border-radius:999px; background:rgba(42,128,128,.16); border:1px solid rgba(42,128,128,.45); color:var(--accent-soft); font-size:.9rem; letter-spacing:.4px; margin-bottom:1.4rem; }
.hero h1 { font-size:clamp(2.2rem, 5vw, 3.6rem); line-height:1.15; font-weight:800; margin-bottom:1rem; }
.hero h1 .hl { color:var(--accent); }
.hero p.lead { font-size:clamp(1.05rem, 2vw, 1.25rem); color:#cfe4e8; max-width:720px; margin:0 auto 1rem; }
.hero p.sub { color:#a9c8cd; max-width:640px; margin:0 auto 2.2rem; font-size:.98rem; }
.btn-row { display:flex; gap:.9rem; justify-content:center; flex-wrap:wrap; }
.btn { display:inline-flex; align-items:center; gap:.55rem; padding:.85rem 1.7rem; border-radius:999px; font-weight:700; font-size:1rem; cursor:pointer; transition:transform .15s, box-shadow .2s, background .2s; border:none; font-family:inherit; }
.btn-primary { background:var(--accent); color:var(--teal-darkest); box-shadow:0 8px 22px rgba(42,128,128,.35); }
.btn-primary:hover { background:var(--accent-soft); transform:translateY(-2px); color:var(--teal-darkest); }
.btn-ghost { background:rgba(255,255,255,.08); color:#fff; border:1px solid rgba(255,255,255,.35); }
.btn-ghost:hover { background:rgba(255,255,255,.16); transform:translateY(-2px); color:#fff; }
.hero-figure { position:relative; z-index:2; margin:3rem auto 0; width:min(860px, 92%); border-radius:24px; overflow:hidden; box-shadow:0 30px 60px rgba(0,0,0,.35); border:1px solid rgba(42,128,128,.25); background:rgba(255,255,255,.04); padding:1.5rem; }

/* sections */
.section { padding:4.5rem 0; }
.section.alt { background:var(--cream); }
.section-head { text-align:center; max-width:760px; margin:0 auto 3rem; }
.section-label { display:inline-block; font-size:.82rem; font-weight:700; letter-spacing:1.2px; text-transform:uppercase; color:var(--teal-mid); background:var(--accent-tint); border:1px solid var(--line); padding:.35rem 1rem; border-radius:999px; margin-bottom:1rem; }
.section-head h2 { font-size:clamp(1.7rem, 3.4vw, 2.4rem); font-weight:800; margin-bottom:.8rem; }
.section-head p { color:var(--ink-soft); }

/* game cards */
.games-grid { display:grid; grid-template-columns:repeat(2, 1fr); gap:2rem; }
.game-card { background:var(--paper); border:1px solid var(--line); border-radius:var(--radius); overflow:hidden; box-shadow:var(--shadow); display:flex; flex-direction:column; transition:transform .2s, box-shadow .25s; }
.game-card:hover { transform:translateY(-6px); box-shadow:var(--shadow-hover); }
.game-thumb { position:relative; aspect-ratio:16/10; overflow:hidden; background:var(--accent-tint); display:grid; place-items:center; }
.game-thumb svg { width:100%; height:100%; }
.game-badge { position:absolute; top:14px; left:14px; background:rgba(18,60,60,.85); color:var(--accent-soft); font-size:.78rem; font-weight:700; letter-spacing:.6px; padding:.3rem .8rem; border-radius:999px; text-transform:uppercase; }
.game-body { padding:1.6rem 1.7rem 1.8rem; display:flex; flex-direction:column; flex:1; }
.game-body h3 { font-size:1.35rem; font-weight:800; margin-bottom:.5rem; }
.game-body h3 a { color:var(--ink); }
.game-body h3 a:hover { color:var(--teal-mid); }
.game-body p { color:var(--ink-soft); font-size:.96rem; margin-bottom:1.1rem; }
.tags { display:flex; flex-wrap:wrap; gap:.45rem; margin-bottom:1.3rem; }
.tag { font-size:.78rem; font-weight:600; color:var(--teal-mid); background:var(--accent-tint); border:1px solid var(--line); padding:.25rem .7rem; border-radius:999px; }
.game-actions { margin-top:auto; display:flex; gap:.7rem; flex-wrap:wrap; }
.btn-play { background:var(--accent); color:var(--teal-darkest); padding:.65rem 1.4rem; font-size:.95rem; }
.btn-play:hover { background:var(--accent-soft); color:var(--teal-darkest); transform:translateY(-2px); }
.btn-learn { background:transparent; color:var(--teal-mid); border:1px solid var(--line); padding:.65rem 1.2rem; font-size:.95rem; }
.btn-learn:hover { background:var(--accent-tint); color:var(--teal-dark); }

/* why grid + prose */
.why-grid { display:grid; grid-template-columns:repeat(3, 1fr); gap:1.6rem; margin-top:1rem; }
.why-card { background:var(--paper); border:1px solid var(--line); border-radius:var(--radius); padding:1.8rem 1.6rem; box-shadow:var(--shadow); text-align:center; }
.why-icon { width:54px; height:54px; margin:0 auto 1rem; border-radius:16px; background:var(--accent-tint); border:1px solid var(--line); display:grid; place-items:center; font-size:1.5rem; }
.why-card h3 { font-size:1.08rem; font-weight:700; margin-bottom:.5rem; }
.why-card p { color:var(--ink-soft); font-size:.92rem; }
.prose { max-width:820px; margin:2.5rem auto 0; color:var(--ink-soft); }
.prose h3 { color:var(--ink); font-size:1.25rem; margin:1.6rem 0 .6rem; }
.prose p { margin-bottom:1rem; }
.prose ul { margin:0 0 1rem 1.2rem; }
.prose li { margin-bottom:.4rem; }

/* ---------- learn page ---------- */
.chapter { background:var(--paper); border:1px solid var(--line); border-radius:var(--radius); box-shadow:var(--shadow); padding:2rem; margin-bottom:2rem; }
.chapter h3 { font-size:1.35rem; font-weight:800; margin-bottom:.4rem; }
.chapter > p { color:var(--ink-soft); max-width:720px; }
.formula-card { display:inline-block; background:var(--accent-tint); border:1px solid var(--line); border-radius:14px; padding:.7rem 1.2rem; font-weight:700; color:var(--teal-dark); margin:1rem 0; font-size:1.05rem; }
.widget { margin-top:1.4rem; border-top:1px dashed var(--line); padding-top:1.4rem; display:grid; grid-template-columns:minmax(260px, 1fr) minmax(220px, 1fr); gap:1.6rem; align-items:center; }
.widget .stage { display:grid; place-items:center; }
.widget .panel { display:flex; flex-direction:column; gap:.8rem; }
.widget .run-total { font-size:1.3rem; font-weight:800; color:var(--teal-dark); }
.ticks { display:flex; flex-wrap:wrap; gap:.4rem; }
.tick { font-weight:700; background:var(--accent-tint); border:1px solid var(--line); border-radius:10px; padding:.2rem .7rem; color:var(--teal-dark); }
.tick.on { background:var(--accent); color:var(--teal-darkest); }
input[type="range"] { accent-color:var(--teal-mid); width:100%; }
.side-btn { font:inherit; font-weight:700; background:var(--accent-tint); color:var(--teal-dark); border:1px solid var(--line); border-radius:999px; padding:.3rem .9rem; cursor:pointer; }
.side-btn:hover { background:var(--accent); color:var(--teal-darkest); }
.real-grid { display:grid; grid-template-columns:repeat(2, 1fr); gap:1.2rem; margin-top:1.2rem; }
.real-card { background:var(--accent-tint); border:1px solid var(--line); border-radius:14px; padding:1.1rem; }
.real-card h4 { font-size:1rem; margin-bottom:.3rem; }
.real-card p { font-size:.92rem; color:var(--ink-soft); }

/* ---------- game shell (all games) ---------- */
.game-hero { color:#fff; background:radial-gradient(900px 400px at 50% -10%, rgba(42,128,128,.22), transparent 60%), linear-gradient(160deg, var(--teal-darkest), var(--teal-dark)); padding:3.2rem 0 2.6rem; text-align:center; }
.game-hero h1 { font-size:clamp(1.8rem, 4vw, 2.6rem); font-weight:800; margin-bottom:.5rem; }
.game-hero p { color:#cfe4e8; max-width:620px; margin:0 auto; }
.game-shell { position:relative; max-width:900px; margin:-1.6rem auto 0; background:var(--paper); border:1px solid var(--line); border-radius:24px; box-shadow:var(--shadow-hover); padding:1.8rem; }
.hud { display:flex; justify-content:space-between; align-items:center; gap:1rem; flex-wrap:wrap; margin-bottom:1.2rem; }
.hud .stat { font-weight:700; color:var(--teal-dark); background:var(--accent-tint); border:1px solid var(--line); border-radius:999px; padding:.35rem 1rem; font-size:.95rem; }
.timer-track { height:10px; background:var(--accent-tint); border-radius:999px; overflow:hidden; border:1px solid var(--line); }
.timer-fill { height:100%; background:var(--accent); border-radius:999px; transition:width .25s linear; }
.timer-fill.low { background:#e8a13c; }
.star-toast { position:absolute; top:16%; left:50%; transform:translateX(-50%); font-size:1.5rem; font-weight:800; color:#8a6508; z-index:60; pointer-events:none; animation:starpop .9s ease-out forwards; }
@keyframes starpop { 0% { opacity:0; transform:translate(-50%, 12px); } 30% { opacity:1; } 100% { opacity:0; transform:translate(-50%, -26px); } }
.options-grid { display:grid; grid-template-columns:repeat(2, 1fr); gap:.8rem; margin-top:1.4rem; }
.option-btn { font:inherit; font-size:1.25rem; font-weight:800; color:var(--teal-dark); background:var(--accent-tint); border:2px solid var(--line); border-radius:16px; padding:1rem; cursor:pointer; transition:transform .12s, background .15s, border-color .15s; }
.option-btn:hover { border-color:var(--teal-mid); transform:translateY(-2px); }
.option-btn.good { background:#d6efdd; border-color:#4d9c66; color:#1e5c33; }
.option-btn.bad { background:#f8dcdc; border-color:#c66; color:#8a2f2f; }
.option-btn .kbd { display:inline-block; font-size:.75rem; font-weight:600; border:1px solid var(--line); border-radius:6px; padding:0 .4rem; margin-right:.5rem; color:var(--ink-soft); background:#fff; }
.stage-box { display:grid; place-items:center; padding:1.2rem; background:var(--cream); border:1px solid var(--line); border-radius:16px; min-height:240px; }
.keypad { display:grid; grid-template-columns:repeat(3, 72px); gap:.6rem; justify-content:center; margin-top:1rem; }
.key { font:inherit; font-size:1.3rem; font-weight:700; color:var(--teal-dark); background:var(--accent-tint); border:1px solid var(--line); border-radius:12px; padding:.7rem 0; cursor:pointer; }
.key:hover { background:var(--accent); color:var(--teal-darkest); }
.answer-box { font:inherit; font-size:1.6rem; font-weight:800; text-align:center; width:130px; border:2px solid var(--line); border-radius:14px; padding:.5rem; color:var(--ink); background:#fff; }
.answer-box.shake { animation:shake .3s; }
@keyframes shake { 25% { transform:translateX(-6px); } 75% { transform:translateX(6px); } }
.overlay { position:absolute; inset:0; background:rgba(247, 244, 238, .96); border-radius:24px; display:grid; place-items:center; text-align:center; padding:2rem; z-index:40; }
.overlay h2 { font-size:1.8rem; font-weight:800; margin-bottom:.6rem; }
.overlay p { color:var(--ink-soft); max-width:460px; margin:0 auto 1.4rem; }
.steps { background:#fff; border:1px solid var(--line); border-radius:14px; padding:1rem 1.4rem; margin:0 auto 1.2rem; max-width:460px; text-align:left; }
.steps div { padding:.25rem 0; font-weight:600; color:var(--teal-dark); }
.stars { font-size:1.4rem; letter-spacing:2px; }
.case-stamp { display:inline-block; border:4px solid #b8860b; color:#8a6508; font-weight:900; letter-spacing:3px; border-radius:10px; padding:.3rem 1rem; transform:rotate(-8deg); margin-bottom:1rem; }
.mode-row { display:flex; gap:.7rem; justify-content:center; margin-bottom:1.2rem; flex-wrap:wrap; }
.mode-btn { font:inherit; font-weight:700; border:2px solid var(--line); background:#fff; color:var(--teal-mid); border-radius:999px; padding:.5rem 1.2rem; cursor:pointer; }
.mode-btn.on { background:var(--teal-mid); color:#fff; border-color:var(--teal-mid); }
.challenge-list { display:grid; gap:.6rem; margin-top:1rem; }
.challenge-row { display:flex; justify-content:space-between; align-items:center; gap:1rem; background:var(--accent-tint); border:1px solid var(--line); border-radius:12px; padding:.6rem 1rem; cursor:pointer; }
.challenge-row:hover { border-color:var(--teal-mid); }
.challenge-row .stars { font-size:1rem; }
.fence-wrap { position:relative; }
#fence-canvas { touch-action:none; width:100%; height:auto; border-radius:14px; border:1px solid var(--line); background:#fbfdfe; cursor:grab; }
.tray { display:flex; align-items:center; justify-content:center; gap:.8rem; margin-top:.9rem; flex-wrap:wrap; }
.tray .seg { width:46px; height:18px; border-radius:9px; background:var(--teal-mid); cursor:grab; }
.hint-text { background:#fffbe6; border:1px solid #eadfa8; border-radius:12px; padding:.8rem 1.1rem; color:#6b5d1f; margin-top:1rem; }

/* footer */
.site-footer { background:var(--teal-darkest); color:#b9d4d9; padding:3.5rem 0 1.6rem; margin-top:4.5rem; }
.footer-grid { display:grid; grid-template-columns:2fr 1fr 1fr; gap:2.5rem; margin-bottom:2.5rem; }
.site-footer h4 { color:#fff; font-size:1rem; margin-bottom:1rem; }
.site-footer p { font-size:.92rem; max-width:340px; }
.footer-links { list-style:none; }
.footer-links li { margin-bottom:.55rem; }
.footer-links a { color:#b9d4d9; font-size:.93rem; }
.footer-links a:hover { color:var(--accent); }
.footer-bottom { border-top:1px solid rgba(42,128,128,.18); padding-top:1.4rem; text-align:center; font-size:.85rem; color:#8fb3ba; }
.footer-bottom a { color:var(--accent-soft); }

/* a11y + motion + responsive */
:focus-visible { outline:3px solid var(--accent); outline-offset:2px; }
@media (prefers-reduced-motion:reduce) {
  html { scroll-behavior:auto; }
  *, *::before, *::after { animation:none !important; transition:none !important; }
}
@media (max-width:900px) {
  .games-grid, .why-grid, .footer-grid, .real-grid, .widget { grid-template-columns:1fr; }
  .options-grid { grid-template-columns:1fr 1fr; }
  .nav-toggle { display:block; }
  .nav-links { display:none; position:absolute; top:100%; right:4%; background:var(--teal-darkest); border:1px solid rgba(42,128,128,.25); border-radius:14px; padding:.8rem; flex-direction:column; align-items:stretch; box-shadow:var(--shadow-hover); min-width:210px; }
  .nav-links.open { display:flex; }
  .nav-links a, .nav-links .lang-btn { display:block; text-align:center; width:100%; }
}

/* Buy Me a Coffee support links */
.nav-links a.nav-support { background:#fbbf24; color:#1a2332; font-weight:700; }
.nav-links a.nav-support:hover { background:#fcd34d; color:#1a2332; }
.footer-support { display:flex; flex-wrap:wrap; align-items:center; justify-content:space-between; gap:1rem; margin:0 0 1.6rem; padding:1.1rem 1.3rem; border:1px solid rgba(42,128,128,.25); border-radius:14px; background:rgba(42,128,128,.08); }
.footer-support h4 { margin:0 0 .3rem; }
.site-footer .footer-support p { max-width:560px; margin:0; }
.footer-support .btn-coffee { display:inline-block; padding:.6rem 1.2rem; border-radius:999px; background:#fbbf24; color:#1a2332; font-weight:700; white-space:nowrap; }
.footer-support .btn-coffee:hover { background:#fcd34d; color:#1a2332; }