[hidden]{display:none!important}
:root{
  --bg:#F3F7F5; --surface:#FFFFFF; --surface-2:#E7EFEC; --code-bg:#F8FBFA;
  --ink:#15232A; --ink-2:#4B5C63; --line:#D3DEDA;
  --jade:#0B6E5A; --jade-hover:#085A49; --jade-ink:#FFFFFF; --jade-soft:#D6EEE6;
  --kw:#2350C2; --fn:#0B6E5A; --str:#B04E14; --num:#8A3AB8; --com:#7A8A90;
  --mark:#FFE27A; --err:#B3261E; --err-soft:#FCE6E4; --warn-soft:#FFF4D1; --warn-line:#E6C04A;
  --shadow:0 1px 2px rgba(21,35,42,.06),0 6px 20px rgba(21,35,42,.05);
  box-sizing:border-box;
  padding-top:env(safe-area-inset-top,0px);
  padding-bottom:env(safe-area-inset-bottom,0px);
}
@media (prefers-color-scheme:dark){
  :root:not([data-theme="light"]){
    --bg:#0E181C; --surface:#15232A; --surface-2:#1C2F37; --code-bg:#0B1417;
    --ink:#E4EDEF; --ink-2:#A1B2B8; --line:#29404A;
    --jade:#3CC4A0; --jade-hover:#5AD6B4; --jade-ink:#05241D; --jade-soft:#123A31;
    --kw:#86ACFF; --fn:#5AD6B4; --str:#F2A56E; --num:#D7A0FF; --com:#7C9097;
    --mark:rgba(255,214,90,.38); --err:#FF8E86; --err-soft:#3A1F1E; --warn-soft:#3A3217; --warn-line:#8A7322;
    --shadow:0 1px 2px rgba(0,0,0,.3),0 6px 20px rgba(0,0,0,.25);
  }
}
:root[data-theme="dark"]{
  --bg:#0E181C; --surface:#15232A; --surface-2:#1C2F37; --code-bg:#0B1417;
  --ink:#E4EDEF; --ink-2:#A1B2B8; --line:#29404A;
  --jade:#3CC4A0; --jade-hover:#5AD6B4; --jade-ink:#05241D; --jade-soft:#123A31;
  --kw:#86ACFF; --fn:#5AD6B4; --str:#F2A56E; --num:#D7A0FF; --com:#7C9097;
  --mark:rgba(255,214,90,.38); --err:#FF8E86; --err-soft:#3A1F1E; --warn-soft:#3A3217; --warn-line:#8A7322;
  --shadow:0 1px 2px rgba(0,0,0,.3),0 6px 20px rgba(0,0,0,.25);
}
*,*::before,*::after{box-sizing:inherit}
html{scroll-padding-top:calc(env(safe-area-inset-top,0px) + 76px);-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font-family:"Lexend",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;font-size:17px;line-height:1.65;font-weight:350}
a{color:var(--jade)}
code,pre,textarea,.mono{font-family:"IBM Plex Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace}
img,svg{max-width:100%}
:focus-visible{outline:3px solid var(--kw);outline-offset:2px;border-radius:6px}
mark{background:linear-gradient(transparent 52%,var(--mark) 52%);color:inherit;padding:0 .1em;font-weight:500}
h1,h2,h3{line-height:1.2;font-weight:600;letter-spacing:-.01em}
h1{font-size:clamp(2rem,4.5vw,2.6rem);margin:.2em 0 .5em}
h2{font-size:1.4rem;margin:2.2em 0 .6em}
h3{font-size:1.1rem;margin:1.6em 0 .4em}
p{margin:.7em 0}
button{font:inherit;color:inherit;cursor:pointer}

/* header */
.top{position:sticky;top:env(safe-area-inset-top,0px);z-index:30;background:color-mix(in srgb,var(--bg) 88%,transparent);backdrop-filter:blur(10px);-webkit-backdrop-filter:blur(10px);border-bottom:1px solid var(--line)}
.top-in{max-width:1320px;margin:0 auto;display:flex;align-items:center;gap:14px;padding:12px 20px;min-height:64px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:var(--ink);font-weight:600;font-size:1.2rem;letter-spacing:-.02em}
.brand svg{width:30px;height:30px;flex:none}
.nav{display:flex;gap:4px;margin-left:18px}
.nav a{text-decoration:none;color:var(--ink-2);padding:8px 12px;border-radius:8px;font-size:.95rem;font-weight:400}
.nav a:hover{color:var(--ink);background:var(--surface-2)}
.nav a.on{color:var(--ink);background:var(--surface-2);font-weight:500}
.top-r{margin-left:auto;display:flex;align-items:center;gap:8px}
.pill{font-size:.85rem;color:var(--ink-2);display:flex;align-items:center;gap:8px;padding:6px 12px;border:1px solid var(--line);border-radius:999px;background:var(--surface);white-space:nowrap}
.pill .bar{width:56px;height:6px;border-radius:9px;background:var(--surface-2);overflow:hidden}
.pill .bar i{display:block;height:100%;background:var(--jade);width:0;transition:width .4s}
.icon-btn{width:40px;height:40px;display:grid;place-items:center;border:1px solid var(--line);background:var(--surface);border-radius:10px;color:var(--ink)}
.icon-btn:hover{background:var(--surface-2)}
.icon-btn svg{width:20px;height:20px}
.menu-btn{display:none}

/* buttons */
.btn{display:inline-flex;align-items:center;gap:8px;border:1px solid transparent;border-radius:9px;padding:9px 16px;font-size:.95rem;font-weight:500;text-decoration:none;line-height:1.2;transition:background .15s}
.btn svg{width:16px;height:16px}
.btn-primary{background:var(--jade);color:var(--jade-ink)}
.btn-primary:hover{background:var(--jade-hover)}
.btn-ghost{background:transparent;color:var(--ink-2);border-color:var(--line)}
.btn-ghost:hover{background:var(--surface-2);color:var(--ink)}
.btn-lg{padding:13px 22px;font-size:1.02rem;border-radius:11px}
.btn[disabled]{opacity:.55;cursor:wait}

/* home */
.hero{max-width:920px;margin:0 auto;padding:48px 20px 32px;display:flex;flex-direction:column;gap:24px}
.hero h1{font-size:clamp(2.3rem,5.4vw,3.7rem);letter-spacing:-.035em;line-height:1.04;margin:0 0 .35em;font-weight:650}
.hero .lead{font-size:1.15rem;color:var(--ink-2);max-width:34em;margin:0 0 1.6em}
.hero .ctas{display:flex;gap:12px;flex-wrap:wrap;justify-content:center}
.hero-demo .runner-box{margin:0;box-shadow:var(--shadow)}
.hero-note{font-size:.85rem;color:var(--ink-2);margin-top:10px}
.band{max-width:1320px;margin:0 auto;padding:40px 20px}
.steps{display:grid;grid-template-columns:repeat(3,1fr);gap:0;border-top:1px solid var(--line)}
.steps li{list-style:none;padding:22px 24px 8px 0}
.steps li+li{padding-left:24px;border-left:1px solid var(--line)}
.steps b{display:block;font-size:1.1rem;font-weight:600;margin-bottom:4px}
.steps .n{display:inline-grid;place-items:center;width:30px;height:30px;border-radius:50%;background:var(--jade-soft);color:var(--jade);font-weight:600;font-size:.9rem;margin-bottom:10px}
.steps p{margin:0;color:var(--ink-2);font-size:.97rem}
.steps{padding:0;margin:0}
.sec-title{font-size:1.7rem;margin:0 0 .3em}
.sec-sub{color:var(--ink-2);margin:0 0 28px;max-width:40em}
.map{display:grid;grid-template-columns:repeat(auto-fill,minmax(340px,1fr));gap:36px 48px}
.map h3{margin:0 0 10px;font-size:1.02rem;color:var(--ink-2);font-weight:500}
.map ol{list-style:none;margin:0;padding:0;border-top:1px solid var(--line)}
.map li a{display:flex;align-items:center;gap:12px;padding:11px 4px;border-bottom:1px solid var(--line);text-decoration:none;color:var(--ink);font-weight:400}
.map li a:hover{background:var(--surface-2)}
.map .num{font-family:"IBM Plex Mono",monospace;font-size:.82rem;color:var(--ink-2);width:22px}
.map .chk{margin-left:auto;width:20px;height:20px;border-radius:50%;border:1.5px solid var(--line);display:grid;place-items:center;flex:none}
.map .done .chk{background:var(--jade);border-color:var(--jade);color:var(--jade-ink)}
.chk svg{width:12px;height:12px;opacity:0}
.done .chk svg{opacity:1}
.dbtables{display:grid;grid-template-columns:repeat(3,1fr);gap:20px}
.dbt{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:18px 20px}
.dbt h3{margin:0 0 4px;font-family:"IBM Plex Mono",monospace;font-size:1.02rem;font-weight:600}
.dbt p{margin:0 0 12px;color:var(--ink-2);font-size:.93rem}
.cols{display:flex;flex-wrap:wrap;gap:6px}
.cols span{font-family:"IBM Plex Mono",monospace;font-size:.8rem;background:var(--surface-2);padding:3px 8px;border-radius:6px}
.foot{border-top:1px solid var(--line);margin-top:40px;padding:28px 20px;text-align:center;color:var(--ink-2);font-size:.9rem}

/* lesson layout */
.shell{max-width:1320px;margin:0 auto;display:grid;grid-template-columns:290px minmax(0,1fr);gap:0}
.side{position:sticky;top:calc(env(safe-area-inset-top,0px) + 65px);align-self:start;height:calc(100vh - 65px - env(safe-area-inset-top,0px));overflow-y:auto;padding:20px 16px 40px 20px;border-right:1px solid var(--line)}
.search{width:100%;padding:10px 12px;border:1px solid var(--line);border-radius:9px;background:var(--surface);color:var(--ink);font:inherit;font-size:.93rem;margin-bottom:14px}
.side h4{font-size:.8rem;font-weight:500;color:var(--ink-2);margin:18px 8px 6px}
.side a{display:flex;align-items:center;gap:8px;padding:7px 10px;border-radius:8px;color:var(--ink);text-decoration:none;font-size:.93rem;font-weight:350;line-height:1.35}
.side a:hover{background:var(--surface-2)}
.side a.on{background:var(--jade-soft);color:var(--ink);font-weight:500;box-shadow:inset 3px 0 0 var(--jade)}
.side a .dot{width:8px;height:8px;border-radius:50%;flex:none;border:1.5px solid var(--line)}
.side a.done .dot{background:var(--jade);border-color:var(--jade)}
.side .empty{color:var(--ink-2);font-size:.9rem;padding:8px}
.content{padding:36px 40px 80px;min-width:0}
.article{max-width:780px}
.crumb{font-size:.9rem;color:var(--ink-2);margin:0}
.article ul,.article ol{padding-left:1.3em}
.article li{margin:.3em 0}
.article code{background:var(--surface-2);padding:1px 6px;border-radius:5px;font-size:.88em}
pre.syntax{background:var(--code-bg);border:1px solid var(--line);border-left:4px solid var(--kw);border-radius:8px;padding:14px 18px;overflow-x:auto;font-size:.93rem;line-height:1.6;margin:1em 0}
.note,.warn{border-radius:10px;padding:14px 18px;margin:1.2em 0;font-size:.97rem}
.note{background:var(--jade-soft)}
.warn{background:var(--warn-soft);border:1px solid var(--warn-line)}
.note p,.warn p{margin:.3em 0}
table.info{border-collapse:collapse;width:100%;margin:1em 0;font-size:.95rem}
.tbl-scroll{overflow-x:auto;margin:1em 0}
.tbl-scroll table.info{margin:0}
table.info th,table.info td{text-align:left;padding:9px 12px;border-bottom:1px solid var(--line);vertical-align:top}
table.info th{font-weight:500;color:var(--ink-2);font-size:.88rem}
table.info td:first-child{font-family:"IBM Plex Mono",monospace;font-size:.88rem;white-space:nowrap;color:var(--kw)}
.joinviz{display:flex;align-items:center;gap:14px;flex-wrap:wrap;margin:1.2em 0}
.jt{background:var(--surface);border:1px solid var(--line);border-radius:10px;overflow:hidden;font-family:"IBM Plex Mono",monospace;font-size:.85rem;min-width:170px}
.jt b{display:block;background:var(--surface-2);padding:6px 12px;font-weight:600}
.jt span{display:block;padding:5px 12px;border-top:1px solid var(--line)}
.jt span.k{background:var(--jade-soft);font-weight:600}
.jarrow{color:var(--jade);font-size:.85rem;text-align:center}
.lesson-foot{display:flex;justify-content:space-between;gap:12px;flex-wrap:wrap;margin-top:48px;padding-top:24px;border-top:1px solid var(--line)}
.lesson-foot .nx{display:flex;flex-direction:column;text-decoration:none;color:var(--ink);padding:10px 14px;border:1px solid var(--line);border-radius:10px;background:var(--surface);max-width:48%}
.lesson-foot .nx small{color:var(--ink-2);font-size:.82rem}
.lesson-foot .nx:hover{border-color:var(--jade)}
.lesson-foot .nx.r{margin-left:auto;text-align:right}
.done-row{display:flex;align-items:center;gap:14px;flex-wrap:wrap;margin-top:36px}
.done-row .msg{color:var(--jade);font-weight:500;font-size:.95rem}

/* runner / editor */
.runner-box{background:var(--surface);border:1px solid var(--line);border-radius:12px;margin:1.1em 0;overflow:hidden}
.rb-head{display:flex;align-items:center;gap:8px;padding:8px 10px 8px 14px;border-bottom:1px solid var(--line);flex-wrap:wrap}
.rb-head .lbl{font-size:.83rem;color:var(--ink-2);margin-right:auto}
.rb-head .btn{padding:6px 12px;font-size:.85rem}
.ed{position:relative;background:var(--code-bg);font-size:.95rem;line-height:1.6}
.ed pre,.ed textarea{margin:0;padding:14px 16px;font-family:"IBM Plex Mono",ui-monospace,Menlo,Consolas,monospace;font-size:inherit;line-height:inherit;white-space:pre-wrap;overflow-wrap:anywhere;word-break:normal;tab-size:2;letter-spacing:0;word-spacing:0;border:0}
.ed pre{position:absolute;inset:0;overflow:hidden;pointer-events:none;color:var(--ink)}
.ed textarea{position:relative;display:block;width:100%;min-height:56px;resize:none;background:transparent;color:transparent;caret-color:var(--ink);overflow:hidden;outline:none}
.ed textarea::selection{background:color-mix(in srgb,var(--kw) 30%,transparent);color:transparent}
.ed:focus-within{box-shadow:inset 0 0 0 2px color-mix(in srgb,var(--kw) 55%,transparent)}
.tk-kw{color:var(--kw);font-weight:600}.tk-fn{color:var(--fn);font-weight:600}.tk-str{color:var(--str)}.tk-num{color:var(--num)}.tk-com{color:var(--com);font-style:italic}
.result{border-top:1px solid var(--line)}
.result:empty{display:none}
.r-meta{font-size:.83rem;color:var(--ink-2);padding:8px 14px;display:flex;gap:10px;align-items:center}
.r-scroll{overflow:auto;max-height:360px}
.r-scroll table{border-collapse:collapse;width:100%;font-size:.88rem}
.r-scroll th,.r-scroll td{color:var(--ink);font-weight:400;padding:7px 14px;text-align:left;border-bottom:1px solid var(--line);white-space:nowrap}
.r-scroll th{position:sticky;top:0;background:var(--surface-2);font-weight:500;font-family:"IBM Plex Mono",monospace;font-size:.82rem}
.r-scroll tr:last-child td{border-bottom:0}
.r-scroll td.n{font-variant-numeric:tabular-nums}
.r-scroll .null{color:var(--com);font-style:italic}
.r-ok{padding:14px;color:var(--jade);font-weight:500;font-size:.95rem;display:flex;gap:10px;align-items:center}
.r-empty{padding:14px;color:var(--ink-2);font-size:.95rem}
.r-err{padding:14px 16px;background:var(--err-soft);color:var(--ink)}
.r-err strong{color:var(--err);font-weight:600}
.r-err p{margin:.3em 0}
.r-err code{display:block;font-size:.8rem;color:var(--ink-2);margin-top:6px;white-space:pre-wrap}
.loading{padding:14px;color:var(--ink-2);font-size:.9rem}

/* exercise + quiz */
.task{border:2px solid var(--jade);border-radius:14px;padding:6px 20px 18px;margin:2.4em 0 1em;background:var(--surface)}
.task h2{margin:14px 0 4px;font-size:1.2rem}
.task .runner-box{margin:14px 0 0}
.feedback{margin-top:12px;padding:12px 14px;border-radius:9px;font-size:.95rem}
.feedback.good{background:var(--jade-soft)}
.feedback.bad{background:var(--err-soft)}
.feedback:empty{display:none}
.hint{margin-top:10px;font-size:.93rem;color:var(--ink-2)}
.hint:empty{display:none}
.quiz{margin:2em 0}
.quiz h2{font-size:1.2rem;margin-bottom:.2em}
.quiz .q{font-weight:500;margin:.4em 0 .8em}
.opts{display:grid;gap:8px}
.opt{text-align:left;padding:11px 14px;border:1.5px solid var(--line);border-radius:10px;background:var(--surface);font-size:.97rem;display:flex;gap:10px;align-items:flex-start;line-height:1.45}
.opt:hover:not([disabled]){border-color:var(--jade)}
.opt .l{font-family:"IBM Plex Mono",monospace;font-size:.85rem;color:var(--ink-2);padding-top:2px}
.opt.right{border-color:var(--jade);background:var(--jade-soft)}
.opt.wrong{border-color:var(--err);background:var(--err-soft)}
.opt[disabled]{cursor:default}

/* playground */
.play{max-width:1320px;margin:0 auto;padding:28px 20px 60px;display:grid;grid-template-columns:270px minmax(0,1fr);gap:28px}
.play h1{font-size:2rem;margin:0 0 .2em}
.play .intro{color:var(--ink-2);margin:0 0 18px}
.schema{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:14px;align-self:start;position:sticky;top:calc(env(safe-area-inset-top,0px) + 84px)}
.schema h3{margin:0 0 8px;font-size:.95rem;color:var(--ink-2);font-weight:500}
.schema details{border-top:1px solid var(--line);padding:6px 0}
.schema summary{cursor:pointer;font-family:"IBM Plex Mono",monospace;font-size:.9rem;font-weight:600;padding:4px 2px;display:flex;justify-content:space-between;align-items:center;gap:8px}
.schema summary .cnt{font-weight:400;color:var(--ink-2);font-size:.78rem}
.schema ul{list-style:none;margin:4px 0 6px;padding:0}
.schema li{display:flex;justify-content:space-between;font-family:"IBM Plex Mono",monospace;font-size:.8rem;padding:2px 4px}
.schema li i{font-style:normal;color:var(--ink-2)}
.schema .view{font-size:.8rem;margin:2px 0 6px;padding:4px 10px}
.examples{display:flex;flex-wrap:wrap;gap:8px;margin:0 0 14px}
.chip{border:1px solid var(--line);background:var(--surface);border-radius:999px;padding:6px 13px;font-size:.85rem}
.chip:hover{border-color:var(--jade);color:var(--jade)}
.play .ed textarea{min-height:200px}

/* cheat */
.cheat{max-width:980px;margin:0 auto;padding:36px 20px 60px}
.cheat h2{font-size:1.2rem;margin:2em 0 .4em}
.cheat table.info td:nth-child(2){font-family:"IBM Plex Mono",monospace;font-size:.85rem;white-space:pre-wrap;color:var(--ink)}

.backdrop{display:none}
@media (max-width:980px){
  .hero{grid-template-columns:1fr;padding-top:36px;gap:32px}
  .dbtables{grid-template-columns:1fr}
  .steps{grid-template-columns:1fr}
  .steps li+li{padding-left:0;border-left:0;border-top:1px solid var(--line)}
  .shell{grid-template-columns:1fr}
  .menu-btn{display:grid}
  .side{position:fixed;left:0;top:calc(env(safe-area-inset-top,0px) + 65px);bottom:0;height:auto;width:min(320px,86vw);z-index:40;background:var(--bg);transform:translateX(-102%);transition:transform .25s;border-right:1px solid var(--line);padding-bottom:calc(40px + env(safe-area-inset-bottom,0px))}
  body.menu-open .side{transform:none}
  body.menu-open .backdrop{display:block;position:fixed;inset:0;z-index:35;background:rgba(0,0,0,.35)}
  .content{padding:24px 18px 60px}
  .play{grid-template-columns:1fr}
  .schema{position:static}
}
@media (max-width:720px){
  .nav{display:none}
  .pill .txt{display:none}
  body{font-size:16px}
  .top-in{padding:10px 14px;gap:8px}
  .lesson-foot .nx{max-width:100%;width:100%}
  .lesson-foot .nx.r{margin-left:0}
  .bottom-nav{display:flex}
}
.bottom-nav{display:none;position:fixed;left:0;right:0;bottom:0;z-index:30;background:var(--surface);border-top:1px solid var(--line);padding-bottom:env(safe-area-inset-bottom,0px)}
.bottom-nav a{flex:1;text-align:center;padding:10px 4px;font-size:.8rem;text-decoration:none;color:var(--ink-2)}
.bottom-nav a.on{color:var(--jade);font-weight:600}
@media (max-width:720px){ body{padding-bottom:56px} }
@media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}

@media (max-width:720px){.rb-head .btn-ghost .bt{display:none}.rb-head .btn-ghost{padding:6px 9px}}