/* jam1e chess — design system
   Layout: Apple-style marketing pages (wide hero, calm sections) + a focused board app. */
:root{
  --bg:#fbfbfd; --bg2:#f5f5f7; --card:#ffffff; --ink:#1d1d1f; --ink2:#424245; --mute:#6e6e73; --line:rgba(0,0,0,.09); --line2:rgba(0,0,0,.05);
  --accent:#2f6bff; --accent-ink:#ffffff; --accent-soft:rgba(47,107,255,.10); --accent-hover:#1f57e6;
  --good:#16a34a; --great:#0ea5e9; --warn:#e3a008; --mist:#f97316; --bad:#e5484d;
  --sq-l:#e7ecf4; --sq-d:#8fa3c4; --hl-last:rgba(255,214,10,.42); --hl-sel:rgba(47,107,255,.38); --dot:rgba(16,24,40,.28); --arrow-user:#f59e0b;
  --shadow:0 1px 2px rgba(0,0,0,.04),0 8px 30px rgba(0,0,0,.06); --shadow-lg:0 30px 80px rgba(18,28,60,.16);
  --nav:rgba(251,251,253,.78);
  --display:"Inter Tight",-apple-system,BlinkMacSystemFont,"SF Pro Display","Segoe UI",system-ui,sans-serif;
  --text:"Inter",-apple-system,BlinkMacSystemFont,"SF Pro Text","Segoe UI",system-ui,sans-serif;
  --mono:"JetBrains Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  --r:18px; --r-sm:12px; --wrap:1180px;
}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){
  --bg:#000; --bg2:#0c0c0f; --card:#151517; --ink:#f5f5f7; --ink2:#d2d2d7; --mute:#98989d; --line:rgba(255,255,255,.11); --line2:rgba(255,255,255,.06);
  --accent:#4f86ff; --accent-soft:rgba(79,134,255,.16); --accent-hover:#6b99ff; --nav:rgba(10,10,12,.72);
  --shadow:0 1px 2px rgba(0,0,0,.4),0 8px 30px rgba(0,0,0,.35); --shadow-lg:0 30px 80px rgba(0,0,0,.6); --dot:rgba(10,14,25,.35);
  color-scheme:dark}}
:root[data-theme="dark"]{
  --bg:#000; --bg2:#0c0c0f; --card:#151517; --ink:#f5f5f7; --ink2:#d2d2d7; --mute:#98989d; --line:rgba(255,255,255,.11); --line2:rgba(255,255,255,.06);
  --accent:#4f86ff; --accent-soft:rgba(79,134,255,.16); --accent-hover:#6b99ff; --nav:rgba(10,10,12,.72);
  --shadow:0 1px 2px rgba(0,0,0,.4),0 8px 30px rgba(0,0,0,.35); --shadow-lg:0 30px 80px rgba(0,0,0,.6); --dot:rgba(10,14,25,.35);
  color-scheme:dark}
:root[data-board="walnut"]{--sq-l:#ecd9b9;--sq-d:#b58863}
:root[data-board="mint"]{--sq-l:#eaf1e6;--sq-d:#7fa58a}
:root[data-board="mono"]{--sq-l:#e6e6ea;--sq-d:#9a9aa3}
:root[data-board="midnight"]{--sq-l:#c5cddc;--sq-d:#4f5d78}

*{box-sizing:border-box}
[hidden]{display:none!important}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*{transition:none!important;animation:none!important}}
body{margin:0;background:var(--bg);color:var(--ink);font-family:var(--text);font-size:17px;line-height:1.55;-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility}
a{color:var(--accent);text-decoration:none}a:hover{text-decoration:underline}
img,svg{max-width:100%}
h1,h2,h3,h4{font-family:var(--display);letter-spacing:-.022em;line-height:1.08;margin:0;text-wrap:balance;color:var(--ink)}
p{margin:0}
.wrap{max-width:var(--wrap);margin:0 auto;padding-left:max(22px,env(safe-area-inset-left,0px));padding-right:max(22px,env(safe-area-inset-right,0px))}
.eyebrow{font-size:13px;font-weight:600;letter-spacing:.09em;text-transform:uppercase;color:var(--accent)}
.mute{color:var(--mute)}
:focus-visible{outline:2.5px solid var(--accent);outline-offset:2px;border-radius:6px}

/* buttons */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;height:44px;padding:0 20px;border-radius:999px;border:1px solid transparent;font:600 15px/1 var(--text);cursor:pointer;transition:background .15s,transform .1s,border-color .15s,color .15s;white-space:nowrap;color:var(--ink);background:var(--bg2);text-decoration:none!important}
.btn:active{transform:scale(.98)}
.btn.primary{background:var(--accent);color:var(--accent-ink)}.btn.primary:hover{background:var(--accent-hover)}
.btn.ghost{background:transparent;border-color:var(--line);color:var(--ink)}.btn.ghost:hover{background:var(--bg2)}
.btn.sm{height:34px;padding:0 14px;font-size:14px}
.btn.lg{height:52px;padding:0 26px;font-size:17px}
.btn[disabled]{opacity:.45;cursor:not-allowed}
.icon-btn{width:38px;height:38px;border-radius:10px;border:0;background:transparent;color:var(--ink);display:inline-grid;place-items:center;cursor:pointer;transition:background .15s}
.icon-btn:hover{background:var(--bg2)}.icon-btn svg{width:20px;height:20px}
.icon-btn[aria-pressed="true"]{background:var(--accent-soft);color:var(--accent)}

/* nav */
body::before{content:"";position:fixed;inset:0 0 auto;height:env(safe-area-inset-top,0px);z-index:60;background:var(--nav)}
.nav{position:sticky;top:env(safe-area-inset-top,0px);z-index:50;background:var(--nav);backdrop-filter:saturate(180%) blur(20px);-webkit-backdrop-filter:saturate(180%) blur(20px);border-bottom:1px solid var(--line2)}
.nav .wrap{display:flex;align-items:center;gap:20px;height:56px}
.brand{display:flex;align-items:center;gap:9px;color:var(--ink);text-decoration:none!important;font-family:var(--display);font-size:19px;letter-spacing:-.02em}
.brand svg{width:28px;height:28px}.brand b{font-weight:700}.brand span{font-weight:300}
.nav-links{display:flex;gap:4px;margin-left:12px}
.nav-links a{color:var(--ink2);font-size:14px;padding:7px 12px;border-radius:999px;text-decoration:none}
.nav-links a:hover{color:var(--ink);background:var(--bg2)}
.nav-links a[aria-current="page"]{color:var(--ink);font-weight:600}
.nav-right{margin-left:auto;display:flex;align-items:center;gap:6px}
.menu-btn{display:none}
@media (max-width:860px){.nav-links{display:none}.menu-btn{display:inline-grid}.nav .btn.cta{display:none}}
.sheet{position:fixed;inset:0;z-index:80;background:var(--bg);padding:calc(env(safe-area-inset-top,0px) + 70px) max(26px,env(safe-area-inset-right,0px)) 30px max(26px,env(safe-area-inset-left,0px));display:flex;flex-direction:column;gap:2px;overflow:auto}
.sheet a{font-family:var(--display);font-size:30px;font-weight:600;color:var(--ink);padding:9px 0;letter-spacing:-.02em}
.sheet .x{position:absolute;top:calc(env(safe-area-inset-top,0px) + 10px);right:max(16px,env(safe-area-inset-right,0px))}

/* footer */
.foot{border-top:1px solid var(--line2);background:var(--bg2);margin-top:96px;padding-block:48px 40px;font-size:14px;color:var(--mute)}
.foot-grid{display:grid;grid-template-columns:1.4fr repeat(3,1fr);gap:32px}
.foot h4{font-family:var(--text);font-size:13px;font-weight:600;color:var(--ink);margin-bottom:10px;letter-spacing:0}
.foot ul{list-style:none;margin:0;padding:0;display:grid;gap:7px}.foot a{color:var(--mute)}.foot a:hover{color:var(--ink)}
.foot .legal{margin-top:36px;padding-top:20px;border-top:1px solid var(--line2);display:flex;flex-wrap:wrap;gap:12px 24px;justify-content:space-between}
@media (max-width:760px){.foot-grid{grid-template-columns:1fr 1fr}.foot-grid>div:first-child{grid-column:1/-1}}

/* board */
.cb{position:relative;width:100%;aspect-ratio:1;user-select:none;-webkit-user-select:none;touch-action:none;border-radius:10px;overflow:hidden;contain:layout}
.cb-sq{position:absolute;inset:0;display:grid;grid-template-columns:repeat(8,1fr);grid-template-rows:repeat(8,1fr)}
.cb-sq>div{position:relative}.cb-sq .l{background:var(--sq-l)}.cb-sq .d{background:var(--sq-d)}
.cb-sq .over{box-shadow:inset 0 0 0 4px rgba(255,255,255,.65)}
.cb-rk,.cb-fl{position:absolute;font:600 clamp(8px,1.5vw,11px)/1 var(--text);pointer-events:none}
.cb-rk{top:4px;left:4px}.cb-fl{bottom:3px;right:4px}
.cb-sq .l .cb-rk,.cb-sq .l .cb-fl{color:var(--sq-d)}.cb-sq .d .cb-rk,.cb-sq .d .cb-fl{color:var(--sq-l)}
.cb-hl,.cb-pcs{position:absolute;inset:0;pointer-events:none}
.cb-hl>div{position:absolute;left:0;top:0;width:12.5%;height:12.5%}
.hl-last{background:var(--hl-last)}.hl-sel{background:var(--hl-sel)}
.hl-check{background:radial-gradient(circle,rgba(229,72,77,.95) 0,rgba(229,72,77,.6) 35%,rgba(229,72,77,0) 72%)}
.hl-dot::after{content:"";position:absolute;inset:37%;border-radius:50%;background:var(--dot)}
.hl-cap::after{content:"";position:absolute;inset:4%;border-radius:50%;border:5px solid var(--dot)}
.hl-mark.m1{background:rgba(245,158,11,.45)}.hl-mark.unsure{box-shadow:inset 0 0 0 3px #f59e0b;background:rgba(245,158,11,.18)}
.pc{position:absolute;left:0;top:0;width:12.5%;height:12.5%;background-size:100%;background-repeat:no-repeat;will-change:transform;pointer-events:none}
.pc.anim{transition:transform .2s cubic-bezier(.2,.7,.2,1)}
.pc.drag{z-index:5;filter:drop-shadow(0 8px 10px rgba(0,0,0,.28));transition:none}
.cb-arrows{position:absolute;inset:0;width:100%;height:100%;pointer-events:none}
.cb-promo{position:absolute;inset:0;background:rgba(0,0,0,.35);z-index:10}
.cb-promo-col{position:absolute;width:12.5%;display:flex;flex-direction:column;background:var(--card);border-radius:10px;box-shadow:var(--shadow-lg);overflow:hidden}
.cb-promo-col button{aspect-ratio:1;border:0;background:var(--card) center/86% no-repeat;cursor:pointer}.cb-promo-col button:hover{background-color:var(--accent-soft)}
.cb[data-mode="edit"] .cb-sq>div{cursor:pointer}

/* generic cards / prose */
.card{background:var(--card);border:1px solid var(--line2);border-radius:var(--r);box-shadow:var(--shadow)}
.chip{display:inline-flex;align-items:center;gap:6px;height:26px;padding:0 10px;border-radius:999px;background:var(--bg2);font-size:13px;font-weight:600;color:var(--ink2);font-variant-numeric:tabular-nums}
.kbd{font:600 12px var(--mono);padding:2px 6px;border-radius:6px;border:1px solid var(--line);background:var(--bg2)}
.seg{display:inline-flex;background:var(--bg2);border-radius:999px;padding:3px;gap:2px}
.seg button{border:0;background:transparent;color:var(--ink2);font:600 13px var(--text);height:30px;padding:0 13px;border-radius:999px;cursor:pointer}
.seg button[aria-pressed="true"]{background:var(--card);color:var(--ink);box-shadow:0 1px 3px rgba(0,0,0,.12)}
input[type=text],input[type=search],textarea,select{font:15px var(--text);color:var(--ink);background:var(--bg2);border:1px solid transparent;border-radius:12px;padding:10px 12px;width:100%;transition:border-color .15s,background .15s}
input:focus,textarea:focus,select:focus{outline:none;border-color:var(--accent);background:var(--card)}
textarea{resize:vertical;min-height:110px;font-family:var(--mono);font-size:13px;line-height:1.5}
label.check{display:inline-flex;align-items:center;gap:7px;font-size:14px;color:var(--ink2);cursor:pointer}
label.check input{width:17px;height:17px;accent-color:var(--accent)}

/* diagrams in articles */
.diagram{margin:28px 0;display:grid;grid-template-columns:minmax(0,340px) minmax(0,1fr);gap:24px;align-items:center}
.diagram .cb{box-shadow:var(--shadow)}
.diagram figcaption{font-size:15px;color:var(--ink2)}
.diagram figcaption b{display:block;font-family:var(--display);font-size:19px;color:var(--ink);margin-bottom:6px;letter-spacing:-.01em}
.diagram figcaption .open{display:inline-block;margin-top:10px;font-weight:600;font-size:14px}
@media (max-width:700px){.diagram{grid-template-columns:1fr}.diagram .cb{max-width:420px}}

/* learn / article */
.l-hero{padding-block:64px 28px}
.l-hero h1{font-size:clamp(38px,6vw,64px);font-weight:700;letter-spacing:-.04em;margin-top:12px}
.l-hero p{font-size:clamp(18px,2vw,21px);color:var(--ink2);margin-top:16px;max-width:52ch;line-height:1.5}
.l-meta{display:flex;gap:14px;flex-wrap:wrap;margin-top:20px;font-size:14px;color:var(--mute)}
.article{display:grid;grid-template-columns:minmax(0,1fr) 230px;gap:56px;align-items:start}
@media (max-width:980px){.article{grid-template-columns:1fr}.toc{display:none}}
.prose{max-width:720px;font-size:18px;line-height:1.7;color:var(--ink2);min-width:0}
.prose h2{font-size:32px;font-weight:700;letter-spacing:-.03em;margin:56px 0 14px;scroll-margin-top:84px}
.prose h3{font-size:22px;font-weight:650;letter-spacing:-.02em;margin:34px 0 10px;color:var(--ink)}
.prose p{margin:0 0 18px}
.prose ul,.prose ol{margin:0 0 20px;padding-left:22px}.prose li{margin-bottom:8px}
.prose strong{color:var(--ink);font-weight:650}
.prose code{font:500 .86em var(--mono);background:var(--bg2);padding:2px 6px;border-radius:6px;color:var(--ink);word-break:break-all}
.prose pre{background:var(--bg2);border-radius:14px;padding:16px 18px;overflow-x:auto;font:500 14px/1.6 var(--mono);color:var(--ink)}
.prose .callout{background:var(--accent-soft);border-radius:16px;padding:18px 20px;margin:24px 0;color:var(--ink)}
.prose .callout b{display:block;margin-bottom:4px}
.prose table{width:100%;border-collapse:collapse;font-size:15px;margin:10px 0 24px}
.prose th,.prose td{text-align:left;padding:10px 12px;border-bottom:1px solid var(--line);vertical-align:top}
.prose th{color:var(--ink);font-weight:600}
.tablewrap{overflow-x:auto}
.toc{position:sticky;top:calc(env(safe-area-inset-top,0px) + 84px);font-size:14px}
.toc b{display:block;font-size:12px;text-transform:uppercase;letter-spacing:.08em;color:var(--mute);margin-bottom:10px}
.toc a{display:block;color:var(--ink2);padding:5px 0 5px 12px;border-left:2px solid var(--line)}
.toc a:hover{color:var(--ink);border-color:var(--accent);text-decoration:none}
.pager{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-top:56px}
.pager a{padding:18px 20px;border-radius:16px;border:1px solid var(--line);color:var(--ink);text-decoration:none!important}
.pager a:hover{border-color:var(--accent)}
.pager span{display:block;font-size:13px;color:var(--mute)}.pager b{font-family:var(--display);font-size:18px;letter-spacing:-.01em}
.pager .next{text-align:right;grid-column:2}
.links{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px;margin:12px 0 28px}
@media (max-width:640px){.links{grid-template-columns:1fr}}
.links a{display:block;padding:16px 18px;border-radius:14px;background:var(--card);border:1px solid var(--line2);box-shadow:var(--shadow);color:var(--ink);text-decoration:none!important;transition:transform .15s}
.links a:hover{transform:translateY(-2px)}
.links a b{display:block;font-size:16px}.links a span{display:block;font-size:14px;color:var(--mute);line-height:1.45;margin-top:4px}
.links a i{font-style:normal;font-size:12px;color:var(--accent);font-weight:600}
.hub{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px}
@media (max-width:900px){.hub{grid-template-columns:1fr 1fr}}@media (max-width:560px){.hub{grid-template-columns:1fr}}
.hub a{display:flex;flex-direction:column;gap:8px;padding:26px;border-radius:22px;background:var(--card);border:1px solid var(--line2);box-shadow:var(--shadow);color:var(--ink);text-decoration:none!important;transition:transform .2s;min-height:190px}
.hub a:hover{transform:translateY(-3px)}
.hub .k{font-size:12px;font-weight:600;text-transform:uppercase;letter-spacing:.08em;color:var(--accent)}
.hub h3{font-size:23px;letter-spacing:-.02em}.hub p{font-size:15px;color:var(--ink2)}
.hub .t{margin-top:auto;font-size:13px;color:var(--mute)}
.hub-sec{margin-top:52px}.hub-sec h2{font-size:28px;letter-spacing:-.03em;margin-bottom:18px}