/* ============================================================
   sections-v3.css  — shared base for the v3 standalone "section" pages
   (tutorials / exercises / tools / roadmap / topic / certification).
   Page-specific bespoke section CSS stays inline per page.
   Dark mode uses html.dark (+ localStorage['theme']) to match the
   site-wide convention; auth slots match www/auth-hydrate.js.
   ============================================================ */

:root{--bg:#f8f9fb;--card:#fff;--ink:#0d1117;--mut:#4b5260;--faint:#5b6573;
  --navy:#1c2c4f;--brand:#1c2c4f;--brand-h:#2d4173;--navy-soft:#eef1f7;
  --accent:#2056d2;--accent-soft:#e9efff;--line:#e4e7ee;--border:#d4d9e3;
  --mast:rgba(255,255,255,.93);--amber:#92590e;--green:#15803d;--red:#9b2c2c;--ease:cubic-bezier(.22,.61,.36,1);
  --paper:#fbfaf7;--code-bg:#11182b}
html.dark{--bg:#0a0f1c;--card:#0f1525;--ink:#eef2fa;--mut:#a5afc4;--faint:#9aa6c0;
  --brand:#5170b3;--brand-h:#6587c4;--navy-soft:#192240;--accent:#7faaff;
  --accent-soft:#1a2748;--line:#1f2a48;--border:#2c3a62;--mast:rgba(11,17,32,.93);
  --green:#7ee8a0;--amber:#f0c47b;--red:#f0a0a0;--paper:#0d1322;--code-bg:#0a1020}

*{box-sizing:border-box;margin:0;padding:0}
body{font-family:'IBM Plex Sans',-apple-system,sans-serif;color:var(--ink);background:var(--bg);
  font-size:16px;line-height:1.62;-webkit-font-smoothing:antialiased;transition:background .25s,color .25s;
  font-feature-settings:"ss01","cv11";text-rendering:optimizeLegibility}
a{color:inherit;text-decoration:none}
.wrap{max-width:1040px;margin:0 auto;padding:0 24px}
h1,h2,h3,h4{font-family:'IBM Plex Serif',Georgia,serif;line-height:1.16;letter-spacing:-.018em}
a:focus-visible,button:focus-visible{outline:none;box-shadow:0 0 0 3px rgba(32,86,210,.24);border-radius:6px}
html.dark a:focus-visible,html.dark button:focus-visible{box-shadow:0 0 0 3px rgba(127,170,255,.26)}
::selection{background:var(--accent-soft);color:var(--ink)}

/* reveal-on-scroll (driven by sections-v3.js; html.js gates it) */
.js .reveal{opacity:0;transform:translateY(13px);transition:opacity .55s var(--ease),transform .55s var(--ease)}
.js .reveal.in{opacity:1;transform:none}
@media(prefers-reduced-motion:reduce){.js .reveal{opacity:1!important;transform:none!important}}

/* ---------- masthead ---------- */
.masthead{position:sticky;top:0;z-index:60;background:var(--mast);
  backdrop-filter:saturate(180%) blur(8px);border-bottom:1px solid var(--line)}
.masthead .wrap{display:flex;align-items:center;gap:16px;height:62px;max-width:1040px}
.wordmark{display:flex;align-items:center;gap:10px;font-family:'IBM Plex Mono',monospace;
  font-weight:600;font-size:15px;color:var(--ink);white-space:nowrap}
.mark{position:relative;display:flex;align-items:center;justify-content:center;width:30px;height:30px;border-radius:8px;background:#16233a;color:#fff;font-family:'Inter Tight','Inter','IBM Plex Sans',sans-serif;font-weight:700;font-size:18px;line-height:1;letter-spacing:-.03em;flex:none}.mark::after{content:'';position:absolute;right:6px;bottom:6px;width:5px;height:5px;border-radius:50%;background:#1f9d5b}html.dark .mark{background:#1b2942}
.co{color:#9fb0d6}
.nav{display:flex;gap:1px;margin-left:6px}
.nav a{padding:7px 11px;border-radius:7px;font-size:13.5px;font-weight:500;color:var(--mut)}
.nav a:hover,.nav a.on{background:var(--navy-soft);color:var(--ink)}
.mh-right{margin-left:auto;display:flex;align-items:center;gap:8px}
.iconbtn{width:34px;height:34px;border-radius:8px;border:1px solid var(--border);background:var(--card);
  cursor:pointer;font-size:15px;display:flex;align-items:center;justify-content:center;color:var(--mut)}
.iconbtn:hover{border-color:var(--navy)}
.btn-pro{display:inline-flex;align-items:center;gap:5px;height:34px;padding:0 13px;border-radius:8px;border:0;
  background:linear-gradient(135deg,#1c2c4f,#33508c);color:#fff;font-size:12.5px;font-weight:600;white-space:nowrap}
.btn-pro:hover{filter:brightness(1.08)}

/* auth slots (auth-hydrate.js fills .auth-user with its own avatar + scoped CSS) */
.auth-anon{display:none}
body.state-anon .auth-anon{display:inline-flex;align-items:center}
.masthead-auth-link{color:var(--mut);font-size:13.5px;font-weight:500;padding:6px 10px;border-radius:7px;white-space:nowrap}
.masthead-auth-link:hover{background:var(--navy-soft);color:var(--ink)}

/* ---------- buttons ---------- */
.btn{display:inline-flex;align-items:center;gap:7px;border-radius:9px;font-size:14px;font-weight:600;
  padding:10px 18px;cursor:pointer;border:1px solid transparent;font-family:inherit;
  transition:transform .13s var(--ease),background .15s,border-color .15s,box-shadow .15s}
.btn-primary{background:var(--brand);color:#fff}
.btn-primary:hover{background:var(--brand-h);transform:translateY(-1px)}
.btn-ghost{background:var(--card);border:1px solid var(--border);color:var(--ink)}
.btn-ghost:hover{border-color:var(--navy)}
.btn-sm{padding:7px 13px;font-size:13px}
.btn:active{transform:translateY(0)}

/* ---------- icons ---------- */
.ic{width:18px;height:18px;flex:none;display:inline-block;vertical-align:middle;color:currentColor}
.ic-sm{width:14px;height:14px}.ic-md{width:22px;height:22px}.ic-lg{width:27px;height:27px}

/* ---------- responsive masthead (hamburger) ---------- */
.mh-burger{display:none}
.nav-cta{display:none}
@media(max-width:760px){
  .masthead .wrap{gap:10px;padding-left:16px;padding-right:16px}
  .mh-burger{display:inline-flex}
  .mh-pro{display:none}
  body.state-anon .mh-signin{display:none}
  /* nav collapses into a full-width dropdown panel below the bar */
  .nav{position:absolute;top:62px;left:0;right:0;flex-direction:column;gap:2px;margin:0;
    background:var(--card);border-bottom:1px solid var(--line);
    box-shadow:0 18px 34px -20px rgba(13,17,23,.55);padding:10px 16px 16px;display:none}
  .masthead.nav-open .nav{display:flex}
  .nav a{padding:11px 12px;border-radius:8px;font-size:15px}
  .nav-cta{display:flex;flex-direction:column;gap:10px;margin-top:10px;padding-top:14px;border-top:1px solid var(--line)}
  .nav-cta .btn-pro{height:42px;justify-content:center;font-size:13.5px}
  .nav-cta .auth-anon{display:none}
  body.state-anon .nav-cta .auth-anon{display:flex}
  .nav-cta .auth-anon{flex:1}
  .nav-cta .masthead-auth-link{flex:1;text-align:center;border:1px solid var(--border);padding:11px}
}