/* Static SEO pages (learn/, challenges/, cert/, 404) */
:root{--bg:#F4F6FA;--sf:#FFFFFF;--sf2:#E9EDF4;--line:#DDE3EC;--fg:#1C2538;--body:#3B4760;--mu:#505C72;--chip:#EEF1F6;--chip-fg:#2B3650;--link:#2563EB;--red:#FF575F;--navy:#1C2538;--term:#0F1626;--term-fg:#E6EDF7;color-scheme:light}
@media (prefers-color-scheme:dark){:root{--bg:#151C2B;--sf:#1C2538;--sf2:#1A2335;--line:#2B3752;--fg:#FFFFFF;--body:#C3CCDB;--mu:#AAB4C8;--chip:#2A3650;--chip-fg:#D5DCE8;--link:#7FB2FF;--navy:#141C2C;color-scheme:dark}}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--body);font:16px/1.65 'Be Vietnam Pro',system-ui,'Segoe UI',sans-serif;overflow-wrap:anywhere}
.wrap{max-width:860px;margin:0 auto;padding:0 20px}
a{color:var(--link)}
h1,h2,h3,h4{color:var(--fg);line-height:1.3;font-family:'Ubuntu','Be Vietnam Pro',sans-serif}
h1{font-size:clamp(1.6rem,4.5vw,2.3rem);margin:.3em 0 .4em}
h2{font-size:1.35rem;margin:1.8em 0 .5em}
h3{font-size:1.1rem}
.top{background:var(--navy);color:#fff;border-bottom:3px solid var(--red)}
.top .wrap{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;padding-top:12px;padding-bottom:12px}
.brand{display:flex;align-items:center;gap:8px;color:#fff;text-decoration:none;font-weight:700;font-family:'Ubuntu',sans-serif;font-size:1.1rem}
.nav{display:flex;gap:16px;flex-wrap:wrap}
.nav a{color:#fff;text-decoration:none;font-size:.95rem;opacity:.9}
.nav a:hover{opacity:1;text-decoration:underline}
main{padding-top:18px;padding-bottom:40px}
.crumbs{font-size:.88rem;color:var(--mu)}
.crumbs a{color:var(--mu)}
.crumbs .sep{opacity:.5}
.kicker{margin:1.2em 0 0;color:var(--mu);font-size:.9rem;text-transform:uppercase;letter-spacing:.04em}
.lead{font-size:1.1rem;color:var(--fg)}
.mu{color:var(--mu);margin:.2em 0 0;font-size:.94rem}
.list{padding-left:1.3em}
.list li{margin:.7em 0}
.list a{font-weight:600}
.no{font-family:'JetBrains Mono',monospace;color:var(--red);font-size:.9em}
.btn{display:inline-block;background:var(--red);color:#fff;text-decoration:none;font-weight:600;padding:.6em 1.1em;border-radius:8px}
.cta{margin:1.4em 0}
.tag{display:inline-block;background:var(--chip);color:var(--chip-fg);border-radius:999px;padding:.05em .65em;font-size:.82rem;margin:0 .3em .3em 0;text-transform:none}
.d-easy{background:#E3F6EC;color:#17623A}.d-medium{background:#FFF4E0;color:#8A5200}.d-hard{background:#FDE8E9;color:#B42832}
code{font-family:'JetBrains Mono',ui-monospace,Consolas,monospace;font-size:.9em;background:var(--chip);color:var(--chip-fg);padding:.1em .35em;border-radius:4px}
pre{background:var(--term);color:var(--term-fg);padding:14px 16px;border-radius:8px;overflow-x:auto;font:14px/1.55 'JetBrains Mono',ui-monospace,Consolas,monospace;white-space:pre}
pre code{background:none;color:inherit;padding:0;font-size:inherit}
pre.mm{background:var(--sf2);color:var(--body);border:1px dashed var(--line)}
blockquote{margin:1em 0;padding:.4em 1em;border-left:4px solid var(--red);background:var(--sf)}
.tbl{overflow-x:auto;margin:1em 0}
table{border-collapse:collapse;width:100%;background:var(--sf);font-size:.94rem}
th,td{border:1px solid var(--line);padding:.5em .7em;text-align:left;vertical-align:top}
th{background:var(--sf2);color:var(--fg)}
.n{text-align:right;white-space:nowrap}
.lesson,.usecase,.brief{background:var(--sf);border:1px solid var(--line);border-radius:10px;padding:4px 22px 14px;margin:1.2em 0}
.usecase h2{margin-top:.9em}
.pn{display:flex;justify-content:space-between;gap:12px;margin:1.6em 0;flex-wrap:wrap}
.pn a{flex:1 1 240px;background:var(--sf);border:1px solid var(--line);border-radius:8px;padding:.7em 1em;text-decoration:none;font-weight:600}
.pn .next{text-align:right}
.foot{border-top:1px solid var(--line);padding:18px 0;font-size:.9rem;color:var(--mu)}
.big{font:700 clamp(4rem,18vw,7rem)/1 'JetBrains Mono',monospace;color:var(--red);margin:.3em 0 0}
@media (max-width:480px){.wrap{padding:0 14px}.lesson,.usecase,.brief{padding:2px 14px 10px}pre{font-size:13px;padding:12px}}