/* Designing Autonomous Worlds · Unreal Engine self-study
   White page, black frame (after diegomuhr.com), one grotesk, black type. */
:root{
  --fg:#000; --bg:#fff; --soft:#f2f2f2; --line:#000; --hair:#d9d9d9; --muted:#555;
  --accent:#1f45ff;          /* diagrams, focus, links on hover */
  --ok:#0b7a3b; --ok-bg:#e6f4ec; --bad:#b3261e; --bad-bg:#fbeaea;
  --frame:.7rem; --gut:clamp(16px,3.2vw,40px);
  --sans:"Inter Tight","Helvetica Neue",Arial,sans-serif;
  --mono:"JetBrains Mono",ui-monospace,Menlo,monospace;
  color-scheme:light;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--fg);font-family:var(--sans);font-size:17px;line-height:1.5;
  font-feature-settings:"ss01","cv11";-webkit-font-smoothing:antialiased}
body::after{content:"";position:fixed;inset:0;border:var(--frame) solid var(--line);pointer-events:none;z-index:50}
::selection{background:var(--fg);color:var(--bg)}
a{color:inherit;text-decoration:underline;text-decoration-thickness:1px;text-underline-offset:.18em}
a:hover{color:var(--accent)}
:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
code{font-family:var(--mono);font-size:.82em;background:var(--soft);padding:.08em .32em;overflow-wrap:anywhere}
kbd{font-family:var(--mono);font-size:.8em;font-weight:600;border:1px solid var(--fg);border-bottom-width:2px;padding:.05em .4em;white-space:nowrap}
.flag{font-family:var(--mono);font-size:.72em;border:1px solid var(--fg);padding:0 .35em;text-transform:uppercase;letter-spacing:.04em}

.wrap{padding:calc(var(--frame) + var(--gut)) calc(var(--frame) + var(--gut)) calc(var(--frame) + 64px)}
.col{max-width:46rem}

/* ---------- index ---------- */
.mast{min-height:min(52vh,460px);display:flex;flex-direction:column;justify-content:flex-end;padding-bottom:clamp(28px,5vw,56px);border-bottom:1px solid var(--line);margin-bottom:8px}
.mast h1{font-weight:800;text-transform:uppercase;font-size:clamp(2.4rem,8.4vw,6rem);line-height:.9;letter-spacing:-.035em;margin:0;text-wrap:balance}
.mast p{font-size:clamp(1.1rem,2.2vw,1.5rem);font-weight:500;margin:.5em 0 0;letter-spacing:-.01em}
.units{list-style:none;margin:0;padding:0}
.unit{display:grid;grid-template-columns:minmax(0,1fr);gap:6px 40px;padding:26px 0 30px;border-bottom:1px solid var(--line)}
@media (min-width:860px){.unit{grid-template-columns:minmax(220px,1fr) minmax(0,1.6fr)}}
.unit h2{font-size:1.5rem;line-height:1.1;font-weight:700;letter-spacing:-.02em;margin:0}
.unit .when{display:block;font-size:.95rem;font-weight:400;color:var(--muted);margin-top:6px;letter-spacing:0}
.unit .now{display:inline-block;font-size:.8rem;font-weight:700;text-transform:uppercase;letter-spacing:.04em;background:var(--fg);color:var(--bg);padding:.15em .45em;margin-top:10px}
.unit ol{list-style:none;margin:0;padding:0;counter-reset:l}
.unit li a{display:grid;grid-template-columns:2.2rem 1fr auto;gap:8px;align-items:baseline;padding:9px 0;border-top:1px solid var(--hair);text-decoration:none;font-size:1.08rem}
.unit li:first-child a{border-top:0;padding-top:2px}
.unit li a:hover{color:var(--fg)}
.unit li a:hover .t{text-decoration:underline;text-underline-offset:.18em}
.unit .n{font-variant-numeric:tabular-nums;color:var(--muted)}
.unit .score{font-size:.85rem;font-variant-numeric:tabular-nums;color:var(--ok);font-weight:600}
.unit.locked h2{color:var(--muted)}
.unit.locked .when{color:var(--fg)}

/* ---------- lesson bar ---------- */
.bar{position:sticky;top:var(--frame);z-index:40;background:var(--bg);border-bottom:1px solid var(--line);
  margin:calc(-1 * var(--gut)) calc(-1 * var(--gut)) 0;padding:12px var(--gut);display:flex;gap:14px;align-items:baseline;justify-content:space-between}
.bar .home{font-weight:800;text-transform:uppercase;letter-spacing:-.01em;text-decoration:none;font-size:.95rem;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.bar .where{font-size:.92rem;font-variant-numeric:tabular-nums;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;min-width:0}
.bar .where b{font-weight:700}
@media (max-width:760px){.bar .home .long{display:none}}
@media (min-width:761px){.bar .home .short{display:none}}

/* ---------- lesson ---------- */
.lhead{padding:clamp(28px,6vw,64px) 0 22px;border-bottom:1px solid var(--line)}
.lhead .of{font-size:.95rem;margin:0 0 10px}
.lhead h1{font-weight:800;font-size:clamp(2rem,5.6vw,3.6rem);line-height:.95;letter-spacing:-.035em;margin:0;text-wrap:balance}
.lhead .pre{margin:14px 0 0;color:var(--muted);font-size:.98rem}
.toc{display:flex;flex-wrap:wrap;gap:4px 18px;margin:16px 0 0;font-size:.92rem}
.toc a{text-decoration:none}
.toc a:hover{text-decoration:underline}
.resume{display:inline-block;margin-top:16px;font-weight:700;font-size:.95rem;border:1px solid var(--fg);padding:.4em .7em;text-decoration:none}
.resume:hover{background:var(--fg);color:var(--bg)}
.resume[hidden]{display:none}

.lesson h2{font-size:1.55rem;line-height:1.1;font-weight:700;letter-spacing:-.02em;margin:2.4em 0 .6em;scroll-margin-top:calc(var(--frame) + 64px);text-wrap:balance}
.lesson h3.sub{font-size:1.15rem;font-weight:700;letter-spacing:-.01em;margin:1.8em 0 .4em}
.lesson p,.lesson li{max-width:68ch}
.lesson p{margin:.7em 0}
.lesson ul,.lesson ol{padding-left:1.15em}
.lesson li{margin:.3em 0}
.step{border-top:1px solid var(--hair);padding-top:18px;margin-top:26px;scroll-margin-top:calc(var(--frame) + 56px)}
.step h3{display:flex;gap:12px;align-items:baseline;font-size:1.18rem;font-weight:700;letter-spacing:-.01em;margin:0 0 6px}
.sn{flex:none;display:inline-grid;place-items:center;min-width:1.7em;height:1.7em;padding:0 .3em;background:var(--fg);color:var(--bg);font-size:.82em;font-weight:700;text-decoration:none;font-variant-numeric:tabular-nums}
.sn:hover{background:var(--accent);color:var(--bg)}
.step.here .sn{background:var(--accent)}

figure{margin:16px 0 22px}
.zoom{display:block;width:100%;padding:0;border:1px solid var(--fg);background:var(--soft);cursor:zoom-in}
.zoom img{display:block;width:100%;height:auto;aspect-ratio:16/9;object-fit:cover}
figcaption{font-size:.9rem;color:var(--muted);margin-top:7px;display:flex;flex-wrap:wrap;gap:4px 12px}
.tempflag{font-family:var(--mono);font-size:.8rem;color:var(--bad)}
.shot-missing{border:1px dashed var(--muted);padding:12px 14px;color:var(--muted);font-size:.92rem}
figure.diagram{border:1px solid var(--fg);padding:16px 16px 12px;margin:20px 0 26px}
.dscroll{overflow-x:auto}
figure.diagram svg{display:block;max-width:100%;height:auto;margin:0 auto;color:var(--fg);font-family:var(--sans)}
figure.diagram figcaption{margin-top:12px;color:var(--fg)}

.tablewrap{overflow-x:auto;max-width:68ch;margin:14px 0}
table{border-collapse:collapse;width:100%;font-size:.96rem}
th,td{text-align:left;padding:8px 12px 8px 0;border-bottom:1px solid var(--hair);vertical-align:top}
th{font-weight:700;border-bottom:1px solid var(--fg)}
.note{border:1px solid var(--fg);padding:12px 14px;margin:18px 0;max-width:68ch;font-size:.96rem}
.lesson blockquote{margin:20px 0;padding:0 0 0 18px;border-left:1px solid var(--fg);max-width:62ch}

fieldset.mcq{border:0;border-top:1px solid var(--hair);padding:16px 0 6px;margin:0;min-width:0}
fieldset.mcq legend{float:left;width:100%;padding:0 0 8px;font-weight:700}
fieldset.mcq legend + *{clear:both}
.qn{font-variant-numeric:tabular-nums;margin-right:10px;color:var(--muted);font-weight:500}
fieldset.mcq label{display:flex;gap:10px;align-items:flex-start;padding:8px 10px;margin:2px 0;cursor:pointer;border:1px solid transparent;max-width:68ch}
fieldset.mcq label:hover{border-color:var(--fg)}
fieldset.mcq input{margin:.28em 0 0;accent-color:var(--fg);width:1.05em;height:1.05em;flex:none}
fieldset.mcq.done label{cursor:default}
fieldset.mcq.done label:hover{border-color:transparent}
fieldset.mcq label.right{background:var(--ok-bg);border-color:var(--ok)}
fieldset.mcq label.wrong{background:var(--bad-bg);border-color:var(--bad)}
.res-tag{margin-left:auto;padding-left:10px;font-weight:700;font-size:.88rem;white-space:nowrap}
label.right .res-tag{color:var(--ok)}
label.wrong .res-tag{color:var(--bad)}
fieldset.mcq.skipped legend::after{content:" (not answered)";font-weight:400;color:var(--muted)}
.why{font-size:.94rem;margin:6px 10px 4px;max-width:66ch}
.quizbar{display:flex;align-items:center;gap:16px;flex-wrap:wrap;margin-top:20px;padding-top:16px;border-top:1px solid var(--hair)}
.btn{font:700 1rem var(--sans);background:var(--fg);color:var(--bg);border:1px solid var(--fg);padding:.6em 1.1em;cursor:pointer}
.btn:hover{background:var(--accent);border-color:var(--accent)}
.quiz-score{font-weight:700;font-size:1.05rem}
.quiz-score:focus{outline:none}

.pager{display:grid;grid-template-columns:1fr 1fr;margin-top:56px;border-top:1px solid var(--line)}
.pager a{padding:16px 0;text-decoration:none;min-width:0}
.pager a small{display:block;font-size:.85rem;color:var(--muted)}
.pager a span{font-weight:700;font-size:1.08rem;letter-spacing:-.01em}
.pager a:hover span{text-decoration:underline}
.pager .next{grid-column:2;text-align:right;padding-left:16px}
.pager .prev{padding-right:16px}
.pager .locked{color:var(--muted)}

dialog.lightbox{border:0;padding:0;margin:0;width:100vw;height:100vh;max-width:none;max-height:none;background:#fff}
dialog.lightbox::backdrop{background:#fff}
.lb-bar{position:sticky;top:0;left:0;display:flex;gap:16px;align-items:baseline;justify-content:space-between;padding:12px 16px;background:#fff;border-bottom:1px solid #000;font-size:.92rem}
.lb-bar span{min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.lb-bar nav{display:flex;gap:16px;flex:none}
.lb-bar button{font:700 .95rem var(--sans);background:none;border:0;padding:0;cursor:pointer;text-decoration:underline;text-underline-offset:.18em}
.lb-scroll{overflow:auto;height:calc(100vh - 46px)}
.lb-scroll img{display:block;max-width:none;width:auto;height:auto;margin:0 auto}
.lb-scroll.fit img{max-width:100%}

footer.foot{border-top:1px solid var(--line);margin-top:72px;padding-top:14px;font-size:.85rem;color:var(--muted)}
footer.foot p{margin:.2em 0;max-width:68ch}

@media (prefers-reduced-motion:no-preference){html{scroll-behavior:smooth}}
@media (max-width:520px){body{font-size:16px}.step h3{font-size:1.08rem}}

/* ---------- lessons menu ---------- */
.bar{flex-wrap:nowrap}
.menubtn{flex:none;display:inline-flex;align-items:center;gap:8px;font:700 .95rem var(--sans);background:var(--bg);color:var(--fg);border:1px solid var(--fg);padding:.32em .65em;cursor:pointer}
.menubtn:hover,.menubtn[aria-expanded="true"]{background:var(--fg);color:var(--bg)}
.menubtn .ico{width:14px;height:10px;border-top:2px solid currentColor;border-bottom:2px solid currentColor;position:relative}
.menubtn .ico::after{content:"";position:absolute;left:0;right:0;top:50%;border-top:2px solid currentColor;transform:translateY(-50%)}
.bar .home{margin-right:auto}
.menu{position:absolute;left:0;right:0;top:100%;background:var(--bg);border-bottom:1px solid var(--fg);max-height:calc(100vh - var(--frame)*2 - 60px);overflow-y:auto;padding:8px var(--gut) 20px;box-shadow:0 18px 30px -18px rgba(0,0,0,.35)}
.menu[hidden]{display:none}
.menu ol{list-style:none;margin:0;padding:0}
.menu .mu{padding:14px 0 8px;border-bottom:1px solid var(--hair)}
.menu .mt{display:block;font-weight:700;font-size:1rem;letter-spacing:-.01em;margin-bottom:4px}
.menu .md{display:block;font-size:.9rem;color:var(--muted)}
.menu .locked .mt{color:var(--muted)}
.menu li a{display:grid;grid-template-columns:1.8rem 1fr;padding:5px 0;text-decoration:none;font-size:.98rem}
.menu li a:hover{text-decoration:underline}
.menu li a .n{color:var(--muted);font-variant-numeric:tabular-nums}
.menu li a[aria-current="page"]{font-weight:700}
.menu li a[aria-current="page"] .n{color:var(--fg)}
.menu .mall{display:inline-block;margin-top:14px;font-weight:700;font-size:.95rem}
@media (min-width:900px){.menu{left:auto;width:min(440px,100%);border-left:1px solid var(--fg)}}

/* ---------- header actions, after-quiz link ---------- */
.lacts{display:flex;flex-wrap:wrap;gap:10px;align-items:center;margin-top:16px}
.lacts .resume{margin-top:0}
.pdf{font:700 .95rem var(--sans);background:var(--bg);color:var(--fg);border:1px solid var(--fg);padding:.4em .7em;cursor:pointer}
.pdf:hover{background:var(--fg);color:var(--bg)}
.afterquiz{margin-top:22px}
.aq{display:flex;flex-direction:column;gap:2px;border:1px solid var(--fg);padding:14px 16px;text-decoration:none;max-width:68ch}
.aq small{font-size:.88rem;color:var(--muted)}
.aq span{font-weight:700;font-size:1.2rem;letter-spacing:-.01em}
.aq span::after{content:" →"}
.aq:hover{background:var(--fg);color:var(--bg)}
.aq:hover small{color:var(--bg)}
.aq .locked::after{content:""}

/* ---------- print / PDF ---------- */
@media print{
  @page{margin:16mm 14mm}
  body{font-size:10.5pt}
  body::after,.bar,.toc,.lacts,.pager,.quizbar,.afterquiz,.foot,dialog,.tempflag{display:none !important}
  .wrap{padding:0}
  .lhead{padding-top:0}
  .lhead h1{font-size:26pt}
  .lesson h2{break-after:avoid;margin-top:1.6em}
  .step h3,.lesson h3.sub{break-after:avoid}
  figure,fieldset.mcq,.note,table{break-inside:avoid}
  .zoom{border:1px solid #000}
  .zoom img{aspect-ratio:auto}
  .dscroll{overflow:visible}
  figure.diagram svg{min-width:0 !important}
  fieldset.mcq label{padding:3px 0}
  .why{display:none}
  a{text-decoration:none}
  .sec-documentation a::after{content:" (" attr(href) ")";font-size:8.5pt;color:#555;word-break:break-all}
}
.printhead{display:none}
@media print{.printhead{display:block;font-size:9pt;font-weight:700;text-transform:uppercase;margin:0 0 10pt}}