/* Learning-guide design v0.5. One typography system for the entire article. */
:root{
 --paper:#fbfbf9;--surface:#ffffff;--ink:#111827;--muted:#4b5563;--faint:#6b7280;--line:#e5e7eb;
 --body:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;
 --heading:'Newsreader',Charter,'Iowan Old Style',Georgia,serif;
 --mono:'JetBrains Mono',ui-monospace,SFMono-Regular,'SF Mono',Menlo,monospace;
 --hand:'Kalam','Comic Sans MS',cursive;
 --accent:#315f91;--accent-hover:#244b76;--tint:#edf3fa;--highlight:#e5eef9;--accent-line:#cbd9e9;
 --code-bg:#192638;--code-ink:#e8edf5;--code-comment:#aebed1;--code-number:#bdd6f5;--code-function:#afd6eb;
}
:root[data-accent="orange"]{
 --accent:#9b5226;--accent-hover:#773b18;--tint:#faf0e8;--highlight:#f5e5d7;--accent-line:#e8d0bd;
 --code-bg:#30251f;--code-ink:#f4ece6;--code-comment:#cbb6a5;--code-number:#edc3a1;--code-function:#edcfb2;
}
*,*::before,*::after{box-sizing:border-box}
html{scroll-behavior:auto;scroll-padding-top:110px;-webkit-text-size-adjust:100%}
body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--body);font-size:20px;font-weight:400;line-height:1.65;-webkit-font-smoothing:antialiased}
button{font:inherit;cursor:pointer}a{color:var(--accent);text-underline-offset:4px;text-decoration-thickness:1px}a:hover{color:var(--accent-hover)}
a:focus-visible,button:focus-visible,summary:focus-visible,.table-scroll:focus-visible{outline:2px solid var(--accent);outline-offset:4px;border-radius:4px}
p{margin:20px 0}strong{font-weight:600}ul,ol{padding-left:25px;margin:20px 0}li{margin:9px 0}
h1,h2,h3{font-family:var(--heading);font-weight:600;color:var(--ink)}h1{font-size:68px;line-height:1.03;letter-spacing:-.028em;margin:25px 0 18px}
h2{font-size:36px;line-height:1.2;letter-spacing:-.02em;border-top:1px solid var(--line);padding-top:29px;margin:68px 0 26px}
h3{font-size:28px;line-height:1.3;letter-spacing:-.014em;margin:38px 0 18px}
h4{font-family:var(--body);font-size:21px;line-height:1.5;margin:28px 0 15px}
.topbar{min-height:76px;position:sticky;top:0;z-index:5;display:flex;justify-content:space-between;align-items:center;gap:22px;padding:16px 32px;border-bottom:1px solid var(--line);background:rgba(251,251,249,.98)}
.brand{font-family:var(--heading);font-size:23px;font-weight:600;line-height:1.2;text-decoration:none;color:var(--ink);white-space:nowrap}.brand-dot{color:var(--accent)}
.header-tools{display:flex;align-items:center;justify-content:flex-end;gap:25px}.links{display:flex;align-items:center;gap:22px}.links a{font-family:var(--mono);font-size:11px;letter-spacing:.06em;text-transform:uppercase;text-decoration:none;color:var(--muted)}.links a:hover{color:var(--accent)}
.palette-toggle{display:inline-flex;align-items:center;border:1px solid var(--line);border-radius:30px;padding:4px;background:var(--surface);gap:3px;flex-shrink:0}.palette-toggle button{display:grid;place-items:center;width:44px;height:44px;border:1px solid transparent;border-radius:50%;background:transparent;padding:9px;color:var(--muted)}.palette-toggle button[aria-pressed="true"]{border-color:var(--accent);background:var(--tint)}.palette-dot{width:24px;height:24px;border-radius:50%;flex-shrink:0}.palette-dot.blue{background:#315f91}.palette-dot.orange{background:#9b5226}
.progress{position:fixed;top:75px;left:0;height:2px;width:0;background:var(--accent);z-index:6;pointer-events:none}
.layout{max-width:1440px;margin:auto;padding:0 36px;display:grid;grid-template-columns:215px minmax(0,960px);gap:65px}
.rail{position:sticky;top:112px;align-self:start;max-height:calc(100vh - 135px);overflow:auto;padding:8px 0 24px}.eyebrow{font-family:var(--mono);font-size:11px;letter-spacing:.13em;color:var(--muted);text-transform:uppercase;font-weight:400}.rail .eyebrow{margin-bottom:20px}.rail nav a{display:flex;gap:12px;padding:9px 13px;border-left:1px solid var(--line);font-size:14px;line-height:1.5;text-decoration:none;color:var(--muted)}.rail nav a span{font-family:var(--mono);font-size:10px;color:var(--faint);padding-top:2px}.rail nav a.active,.rail nav a:hover{border-left:2px solid var(--accent);background:var(--tint);color:var(--accent)}.rail .note{border-top:1px solid var(--line);padding-top:20px;margin-top:26px;color:var(--muted);font-size:14px;line-height:1.7}.rail button{background:transparent;border:1px solid var(--accent-line);border-radius:24px;padding:9px 13px;font-size:13px;color:var(--accent);margin-top:14px}
main{min-width:0;padding:60px 0 100px}.hero-kicker{display:flex;align-items:center;gap:12px}.hero-kicker::before{content:'';width:24px;height:1px;background:var(--accent)}
main>p:first-of-type{font-family:var(--heading);font-size:25px;line-height:1.45;color:var(--muted);margin:0 0 24px}main>p:nth-of-type(2){font-family:var(--mono);font-size:11.5px;line-height:1.9;color:var(--muted);letter-spacing:.07em;text-transform:uppercase;border-bottom:1px solid var(--line);padding-bottom:28px;margin-bottom:32px;max-width:none}main>p:nth-of-type(2) strong{font-weight:500}
main>p,main>ul,main>ol{max-width:78ch}
.hand-note,blockquote p{font-family:var(--hand);font-size:21px;line-height:1.75;color:var(--ink);font-weight:400;background:none;border:none;padding:0;margin:25px 0}.hand-note{max-width:76ch}.hand-note code{font-size:.76em;color:inherit;background:none;padding:0}blockquote{padding:0;margin:24px 0;border:0;background:none}
mark{color:var(--ink);background:var(--highlight);padding:.04em .16em;border-radius:.15em;box-decoration-break:clone;-webkit-box-decoration-break:clone}.pencil-underline{text-decoration:underline;text-decoration-color:var(--accent);text-underline-offset:5px}.pencil-circle{border:1px solid currentColor;border-radius:48%;padding:0 .25em}
/* Tables use one readable size, including those inside revealed solutions. */
.table-scroll{width:100%;overflow-x:auto;margin:28px 0 32px;border:1px solid var(--line);border-radius:9px;background:var(--surface);-webkit-overflow-scrolling:touch}
table{width:100%;min-width:680px;border-collapse:collapse;font-family:var(--body);font-size:18px;line-height:1.7;color:var(--ink);text-align:left}
th,td{padding:19px 23px;vertical-align:top;text-align:left;font-family:var(--body)}
th{font-size:17px;font-weight:600;line-height:1.6;letter-spacing:0;color:var(--ink);background:var(--tint);border-bottom:1px solid var(--accent-line)}
td{border-top:1px solid var(--line)}tbody tr:nth-child(even) td{background:#fafbfc}
th:first-child,td:first-child{min-width:145px}td:first-child code{white-space:nowrap;overflow-wrap:normal;word-break:normal}table code{font-size:.88em;line-height:1.6;padding:2px 4px}
code{font-family:var(--mono);font-weight:400;font-size:.84em;line-height:inherit;font-variant-ligatures:none;background:var(--tint);color:var(--accent);padding:2px 5px;border-radius:4px;overflow-wrap:anywhere}
.cell{margin:27px 0;border:1px solid var(--accent-line);border-radius:9px;overflow:hidden;background:var(--surface)}.cell-bar{display:flex;align-items:center;justify-content:space-between;gap:16px;padding:11px 17px;background:var(--tint);border-bottom:1px solid var(--accent-line);color:var(--muted);font-family:var(--mono);font-size:11px;line-height:1.5}.cell-bar .kind{font-family:var(--mono);font-size:10px;letter-spacing:.08em;text-transform:uppercase;display:flex;align-items:center;gap:8px}.cell-bar .kind::before{content:'';width:6px;height:6px;border-radius:50%;background:var(--accent)}
.cell pre{padding:23px 24px;margin:0;border:0;background:var(--code-bg);overflow:auto;line-height:1.85}.cell pre code{font-family:var(--mono);font-size:15px;line-height:1.85;white-space:pre;color:var(--code-ink);background:none;padding:0;overflow-wrap:normal}.cell.output pre{background:var(--paper)}.cell.output pre code{color:var(--ink);font-size:14.5px}.cell .copy{font-family:var(--body);font-size:12px;line-height:1.4;padding:4px 10px;border:1px solid var(--accent-line);border-radius:5px;background:var(--surface);color:var(--accent)}
.tok-comment{color:var(--code-comment);font-style:italic}.tok-string{color:#e4c6a0}.tok-keyword{color:#d0bfe6}.tok-number{color:var(--code-number)}.tok-function{color:var(--code-function)}
figure{margin:32px 0}figure img{display:block;width:100%;height:auto;border:0;border-radius:8px}figcaption{display:flex;justify-content:space-between;gap:20px;color:var(--faint);font-family:var(--body);font-size:13px;margin-top:9px}
/* Body text never shrinks when an answer is expanded. */
details{font-family:var(--body);font-size:inherit;line-height:inherit;margin:23px 0;padding:0 25px;background:var(--surface);border:1px solid var(--line);border-radius:9px}
summary{cursor:pointer;font-family:var(--body);font-size:18px;line-height:1.6;font-weight:600;color:var(--accent);padding:20px 0}
details[open] summary{border-bottom:1px solid var(--line);margin-bottom:24px}details p,details li{font-family:var(--body);font-size:inherit;line-height:inherit}details p{margin:23px 0}details table{font-family:var(--body);font-size:18px;line-height:1.7}details .table-scroll{margin:26px 0 30px}details .cell{margin:25px 0}
footer{display:flex;justify-content:space-between;gap:20px;border-top:1px solid var(--line);padding-top:25px;margin-top:55px;font-family:var(--body);font-size:14px;color:var(--muted)}footer a{text-decoration:none}
@media(max-width:1120px){.layout{display:block;max-width:1040px;padding:0 30px}.rail{display:none}.topbar{padding:15px 25px}.header-tools{gap:20px}.links{gap:17px}}
@media(max-width:760px){body{font-size:18px;line-height:1.7}.topbar{padding:12px 19px;min-height:76px;gap:12px}.brand{font-size:21px}.header-tools{gap:14px}.links{gap:12px}.links a{font-size:10px}.layout{padding:0 22px}main{padding-top:37px}h1{font-size:49px}h2{font-size:31px;margin-top:53px}h3{font-size:26px}main>p:first-of-type{font-size:23px}main>p:nth-of-type(2){font-size:10.5px}.hand-note{font-size:20px}.cell pre{padding:20px 18px}.cell pre code{font-size:14px}.cell.output pre code{font-size:13.5px}table,details table{font-size:17px}th{font-size:17px}th,td{padding:17px 19px}details{padding:0 18px}summary{font-size:17px}figcaption{font-size:12px}footer{flex-direction:column}}
@media(max-width:580px){.topbar{flex-wrap:wrap;gap:9px 14px}.links{display:none}.header-tools{margin-left:auto}.brand{font-size:20px}.layout{padding:0 18px}main{padding-top:32px}h1{font-size:46px}.palette-toggle{padding:3px}table{min-width:640px}.cell-bar{padding:10px 13px}.cell-bar .kind{font-size:9px}}
@media print{.topbar,.rail,.progress,.copy,.palette-toggle{display:none}body{background:white;color:black;font-size:11pt}.layout{display:block;padding:0;max-width:none}main{padding:0}h1{font-size:38pt}h2{font-size:23pt}h3{font-size:17pt}.table-scroll{overflow:visible}table,details table{min-width:0;font-size:10pt}th{font-size:10pt}th,td{padding:9px}.cell pre code{font-size:9pt;white-space:pre-wrap}figure,.hand-note{break-inside:avoid}}