/* Lesson 12 (the scientific calculator), shared by en.html and index.html.
   The replica keeps the real app's own dark colours in both page themes. */
:root{
  --calc-win:#0d0f14; --calc-card:#151922; --calc-text:#f3f5fa; --calc-muted:#7b8396; --calc-accent:#a399ff; --calc-err:#ff7a8f; --calc-chip:#1f2433;
  --k-function:#191d27; --k-function-fg:#aeb6cc; --k-control:#191d27; --k-control-fg:#a399ff;
  --k-clear:#341b26; --k-clear-fg:#ff8fa3; --k-digit:#252a37; --k-digit-fg:#f3f5fa;
  --k-operator:#2a2552; --k-operator-fg:#c9c1ff; --k-equals:linear-gradient(#a091ff,#6c5cf3); --k-equals-fg:#fff;
}

/* Parts A–D of the lesson */
.subnav{display:flex;flex-wrap:wrap;gap:.4rem}
.subnav a{font-family:var(--f-code);font-size:.8rem;text-decoration:none;color:var(--ink);padding:.35rem .75rem;border-radius:999px;background:var(--hl-soft);border:1px solid var(--line)}
.subnav a:hover{border-color:var(--muted)}
h3.part{display:flex;align-items:center;gap:.6rem;font-size:1.45rem;font-weight:800;margin-top:1.4rem;scroll-margin-top:4rem}
h3.part .tag{flex:none;width:2.1rem;height:2.1rem;border-radius:9px;display:grid;place-items:center;background:var(--ink);color:var(--bg);font-size:1rem}
.lesson h4{font-family:var(--f-display);font-weight:600;font-size:1.05rem;margin:.6rem 0 0}
kbd{font-family:var(--f-code);font-size:.8em;border:1px solid var(--line);border-bottom-width:2.5px;border-radius:6px;padding:.05em .4em;background:var(--surface);white-space:nowrap}

/* Numbered how-to steps */
.steps{list-style:none;margin:0;padding:0;display:grid;gap:.7rem;counter-reset:step;max-width:none}
.steps>li{counter-increment:step;display:grid;grid-template-columns:2.1rem minmax(0,1fr);gap:.8rem;align-items:start;background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:.8rem .9rem}
.steps>li::before{content:counter(step);width:2.1rem;height:2.1rem;border-radius:50%;display:grid;place-items:center;background:var(--blue);color:var(--surface);font-family:var(--f-display);font-weight:800}
.steps>li>div{display:grid;gap:.45rem;min-width:0}
.steps pre.py{font-size:.85rem;padding:.6rem .9rem}
.terminal{margin:0;background:#0b0f19;color:#d7deea;border-radius:12px;padding:.8rem 1rem;font-family:var(--f-code);font-size:.8rem;line-height:1.55;overflow-x:auto;white-space:pre}
.terminal .ok{color:#4cc38a;font-weight:600}
.terminal .dim{color:#7d8ba8}

/* Annotated screenshot */
.shot{margin:0;display:grid;gap:.8rem}
.shot .frame{position:relative;border-radius:12px;overflow:hidden;box-shadow:0 18px 40px -24px rgba(10,15,30,.7);background:var(--calc-win)}
.shot img{display:block;width:100%;height:auto}
.pin{position:absolute;transform:translate(-50%,-50%);width:1.7rem;height:1.7rem;border-radius:50%;display:grid;place-items:center;background:var(--hl);color:#16213A;font-family:var(--f-display);font-weight:800;font-size:.85rem;border:2px solid #16213A;box-shadow:0 2px 8px rgba(0,0,0,.45)}
@media (max-width:560px){.pin{width:1.3rem;height:1.3rem;font-size:.7rem;border-width:1.5px}}
.pins{list-style:none;margin:0;padding:0;display:grid;gap:.45rem;max-width:none}
@media (min-width:700px){.pins{grid-template-columns:1fr 1fr;column-gap:1.4rem}}
.pins li{display:grid;grid-template-columns:1.7rem minmax(0,1fr);gap:.6rem;align-items:start;font-size:.93rem}
.pins li b.n{width:1.7rem;height:1.7rem;border-radius:50%;display:grid;place-items:center;background:var(--hl);color:#16213A;font-family:var(--f-display);font-weight:800;font-size:.85rem}

/* Key guide table */
.keyname{font-family:var(--f-code);white-space:nowrap}
.sheet td .kchip{display:inline-block;min-width:1.9rem;text-align:center;padding:.1rem .4rem;margin:.1rem .1rem .1rem 0;border-radius:6px;font-family:var(--f-body);font-size:.82rem;background:var(--kb);color:var(--kf)}

/* Replica of the app */
.calc-grid{display:grid;gap:1rem}
@media (min-width:860px){.calc-grid{grid-template-columns:minmax(0,24rem) minmax(0,1fr)}}
.calc-grid>*{min-width:0}
.calc{background:var(--calc-win);border-radius:16px;padding:.6rem;display:grid;gap:.5rem;align-content:start}
.calc-screen{background:var(--calc-card);border-radius:12px;padding:.55rem .8rem .5rem;display:grid;gap:.15rem}
.calc-screen.shake{animation:shake .24s ease}
@keyframes shake{20%{transform:translateX(7px)}40%{transform:translateX(-6px)}60%{transform:translateX(4px)}80%{transform:translateX(-2px)}}
.calc-info{display:flex;gap:.35rem;align-items:center;font-size:.72rem;color:var(--calc-muted);font-family:var(--f-code);min-height:1.3rem}
.calc-info .chip{background:var(--calc-chip);color:var(--calc-accent);border-radius:6px;padding:.05rem .45rem;font-weight:600;white-space:pre}
#calcMsg{margin-left:auto;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;text-align:right;min-width:0}
#calcMsg.err{color:var(--calc-err)}
#calcDisplay{all:unset;box-sizing:border-box;width:100%;text-align:right;font-family:var(--f-body);font-weight:300;font-size:1.9rem;color:var(--calc-text);caret-color:var(--calc-accent)}
#calcDisplay:focus-visible{outline:2px solid var(--calc-accent);outline-offset:4px;border-radius:4px}
#calcPreview{min-height:1.4rem;text-align:right;font-family:var(--f-body);font-size:1rem;color:var(--calc-accent);overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.calc-keys{display:grid;grid-template-columns:repeat(4,minmax(0,1fr)) 5px repeat(4,minmax(0,1fr));gap:4px}
.calc-keys button{min-height:2.35rem;padding:.2rem 0;border:0;border-radius:8px;font-size:.8rem;font-family:var(--f-body);font-weight:400;background:var(--kb);color:var(--kf);transition:filter .1s}
.calc-keys button:hover{filter:brightness(1.3)}
.calc-keys button:active,.calc-keys button.flash{filter:brightness(1.6)}
.calc-keys .k-digit,.calc-keys .k-operator{font-size:1rem}
.calc-keys .k-equals{font-size:1.1rem;font-weight:600}
.k-function{--kb:var(--k-function);--kf:var(--k-function-fg)} .k-control{--kb:var(--k-control);--kf:var(--k-control-fg)}
.k-clear{--kb:var(--k-clear);--kf:var(--k-clear-fg)} .k-digit{--kb:var(--k-digit);--kf:var(--k-digit-fg)}
.k-operator{--kb:var(--k-operator);--kf:var(--k-operator-fg)} .k-equals{--kb:var(--k-equals);--kf:var(--k-equals-fg)}

/* Every step of one calculation */
.pipe{display:grid;gap:.6rem;align-content:start}
.stage{display:grid;grid-template-columns:1.8rem minmax(0,1fr);gap:.6rem;align-items:start}
.stage .num{width:1.8rem;height:1.8rem;border-radius:50%;display:grid;place-items:center;background:var(--blue-soft);color:var(--blue);font-family:var(--f-code);font-size:.75rem;font-weight:600}
.stage .body{display:grid;gap:.25rem;min-width:0}
.stage .fn-name{font-family:var(--f-code);font-size:.76rem;color:var(--muted)}
.stage .show{font-family:var(--f-code);font-size:.9rem;overflow-wrap:anywhere;white-space:pre-wrap}
.stage.bad .num{background:var(--bad);color:var(--surface)}
.stage.bad .show{color:var(--bad)}
.stage.off{opacity:.4}
.toks{display:flex;flex-wrap:wrap;gap:.3rem}
.tok{display:inline-flex;flex-direction:column;align-items:center;font-family:var(--f-code);font-size:.85rem;border-radius:6px;padding:.05rem .45rem;border:1.5px solid var(--tc);background:var(--surface)}
.tok small{font-size:.58rem;letter-spacing:.06em;text-transform:uppercase;color:var(--tc)}
.tok.number{--tc:var(--t-int)} .tok.name{--tc:var(--t-func)} .tok.op{--tc:var(--muted)}
.tree{font-family:var(--f-code);font-size:.85rem;overflow-x:auto;padding-block:.2rem}
.node{display:inline-flex;align-items:center;gap:.3rem;flex-wrap:wrap;border:1.5px solid var(--blue);border-radius:10px;padding:.2rem .4rem;background:var(--surface);vertical-align:middle}
.node .node{background:var(--sunk)}
.node .node .node{background:var(--surface)}
.node .op{color:var(--blue);font-weight:600}
.node .nv{font-size:.68rem;background:var(--hl);color:#16213A;border-radius:999px;padding:0 .4rem;font-weight:600;font-style:normal}
.leaf{display:inline-block;padding:.05rem .35rem;border-radius:5px;background:var(--blue-soft)}
.leaf small{color:var(--muted);font-size:.68rem;margin-left:.25rem}
.paren{color:var(--muted)}
.node .op.imp{opacity:.55;font-style:italic}
.stage small{color:var(--muted);font-size:.78rem}
.order{margin:0;padding-left:1.4rem;font-family:var(--f-code);font-size:.82rem;display:grid;gap:.15rem}

/* Big picture: window → engine → answer */
.flow{display:grid;gap:.5rem;align-items:stretch}
@media (min-width:760px){.flow{grid-template-columns:minmax(0,1fr) auto minmax(0,1.25fr) auto minmax(0,1fr)}}
.flow .box{border:1.5px solid var(--line);border-radius:12px;background:var(--surface);padding:.75rem .85rem;display:grid;gap:.3rem;align-content:start}
.flow .box h4{margin:0;font-size:1rem}
.flow .box p{font-size:.88rem}
.flow .box.engine{border-color:var(--blue);background:var(--blue-soft)}
.flow .box ol{margin:0;padding-left:1.1rem;font-size:.86rem;display:grid;gap:.15rem}
.flow .arrow{align-self:center;justify-self:center;font-family:var(--f-code);color:var(--muted);font-size:.78rem;text-align:center;line-height:1.3}
.flow .arrow b{display:block;font-size:1.3rem;color:var(--blue)}
@media (max-width:759px){.flow .arrow b{transform:rotate(90deg)}}

/* Map of the file */
.fmap{display:flex;height:2.2rem;border-radius:8px;overflow:hidden;gap:2px}
.fmap span{min-width:3px}
.seg-setup{background:var(--muted)} .seg-engine{background:var(--blue)} .seg-help{background:var(--ok)} .seg-draw{background:var(--t-func)} .seg-gui{background:var(--hl)}
.fmap-list{display:grid;gap:.4rem;font-size:.9rem}
.fmap-list>div{display:grid;grid-template-columns:.8rem 5.6rem minmax(0,1fr);gap:.6rem;align-items:baseline}
.fmap-list i{width:.8rem;height:.8rem;border-radius:3px;display:inline-block;align-self:center}
.fmap-list .lines{font-family:var(--f-code);font-size:.78rem;color:var(--muted);font-variant-numeric:tabular-nums}

/* Precedence ladder */
.ladder{display:grid;gap:.35rem}
.rung{display:flex;flex-wrap:wrap;align-items:baseline;gap:.2rem .8rem;border:1px solid var(--line);border-radius:10px;padding:.5rem .7rem;background:var(--surface);margin-left:calc(var(--i) * .7rem)}
.rung b{font-family:var(--f-code);font-size:.85rem;color:var(--blue);min-width:4.2rem}
.rung .ops{font-family:var(--f-code);font-size:.95rem;font-weight:600}
.rung small{color:var(--muted);font-size:.85rem}

/* Key colour swatches */
.swatches{display:flex;flex-wrap:wrap;gap:.6rem}
.sw{display:grid;gap:.2rem;justify-items:center;font-family:var(--f-code);font-size:.72rem;color:var(--muted)}
.sw b{width:3.4rem;height:2.3rem;border-radius:8px;display:grid;place-items:center;font-size:.85rem;font-weight:400;background:var(--kb);color:var(--kf)}

/* Before/after bar for the resize speed-up */
.bars{display:grid;gap:.45rem;max-width:34rem}
.bar{display:grid;grid-template-columns:7.5rem minmax(0,1fr);gap:.6rem;align-items:center;font-size:.85rem}
.bar span{height:1.4rem;border-radius:6px;display:flex;align-items:center;justify-content:flex-end;padding-right:.45rem;font-family:var(--f-code);font-size:.75rem;font-weight:600;color:#16213A}
.bar .slow{background:var(--bad-soft);border:1px solid var(--bad)}
.bar .fast{background:var(--ok-soft);border:1px solid var(--ok)}

/* Test runner */
.tests-sum{display:flex;align-items:center;gap:.8rem;flex-wrap:wrap}
.tests-sum .big{font-family:var(--f-display);font-weight:800;font-size:1.4rem}
.pass{color:var(--ok);font-weight:600} .fail{color:var(--bad);font-weight:600}
.sheet td.mono{font-family:var(--f-code);font-size:.8rem;overflow-wrap:anywhere}

/* Explain it */
.pitch{border-left:4px solid var(--blue);background:var(--blue-soft);border-radius:0 12px 12px 0;padding:.9rem 1.1rem;display:grid;gap:.4rem;max-width:65ch}
.pitch p{font-size:1.02rem}
.script{margin:0;padding:0;list-style:none;display:grid;gap:.6rem;counter-reset:demo;max-width:none}
.script>li{counter-increment:demo;display:grid;grid-template-columns:2rem minmax(0,1fr);gap:.4rem .8rem;background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:.7rem .9rem}
.script>li::before{content:counter(demo);grid-row:span 2;width:2rem;height:2rem;border-radius:50%;display:grid;place-items:center;background:var(--hl);color:#16213A;font-family:var(--f-display);font-weight:800}
.script .do{font-size:.92rem}
.script .say{font-size:.92rem;color:var(--muted)}
.script .say::before{content:"“";color:var(--blue);font-weight:600}
.script .say::after{content:"”";color:var(--blue);font-weight:600}
.qa{display:grid;gap:.5rem}
.qa details{border:1px solid var(--line);border-radius:12px;background:var(--surface);padding:.75rem 1rem}
.qa summary{cursor:pointer;font-weight:600;font-family:var(--f-display);font-size:1.02rem}
.qa summary::marker{color:var(--blue)}
.qa details>div{display:grid;gap:.5rem;margin-top:.55rem}
.qa details p{font-size:.94rem}
.checklist{list-style:none;padding:0 !important}
.checklist li{display:grid;grid-template-columns:1.4rem minmax(0,1fr);gap:.4rem}
.checklist li::before{content:"☐";color:var(--blue);font-size:1.05rem;line-height:1.5}