/* === Crosswalk Tutorial • Modern Stylesheet (drop-in replacement) === */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;600;700&display=swap');

/* Palettes */
:root{
  --bg:#0b1220; --panel:#121a2b; --text:#e6eefb; --muted:#9fb3d9;
  --accent:#7aa2ff; --accent2:#3dd2c3; --border:#1f2a44;
  --chip:#122345; --chipText:#bcd3ff; --ring:#2a7fff33;
}
[data-theme="light"]{
  --bg:#f7f9fc; --panel:#ffffff; --text:#0f172a; --muted:#5b6b88;
  --accent:#2a66ff; --accent2:#10bfa7; --border:#e6eaf3;
  --chip:#e9f0ff; --chipText:#21407a; --ring:#2a66ff22;
}

/* Resets / base */
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0; font-family:Inter,system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,sans-serif;
  background:
    radial-gradient(1000px 340px at 20% -10%, color-mix(in hsl, var(--accent) 28%, transparent), transparent),
    radial-gradient(1000px 360px at 85% -10%, color-mix(in hsl, var(--accent2) 28%, transparent), transparent),
    var(--bg);
  color:var(--text); line-height:1.6;
}
a{color:var(--accent); text-underline-offset:3px}
a:focus-visible, button:focus-visible{outline:2px solid var(--accent); outline-offset:3px; border-radius:8px}
.wrapper{max-width:1100px; margin:0 auto; padding:0 16px}

/* Header / Nav */
header{
  position:sticky; top:0; z-index:20;
  background:color-mix(in hsl, var(--bg) 82%, transparent);
  backdrop-filter:blur(8px);
  border-bottom:1px solid var(--border)
}
.nav{display:flex; gap:12px; align-items:center; padding:10px 0; flex-wrap:wrap}
.nav a{
  position:relative; padding:8px 12px; border-radius:12px; text-decoration:none; color:var(--text)
}
.nav a::after{
  content:""; position:absolute; left:12px; right:12px; bottom:4px; height:2px;
  background:linear-gradient(90deg,var(--accent),var(--accent2));
  opacity:0; transform:scaleX(.6); transition:.22s ease
}
.nav a:hover::after, .nav a.active::after{opacity:1; transform:scaleX(1)}
.nav .spacer{flex:1 1 auto}

/* Buttons */
.btn,.btn-icon{
  display:inline-flex; align-items:center; justify-content:center; gap:8px;
  padding:10px 14px; border-radius:12px; border:1px solid color-mix(in hsl, var(--border) 80%, transparent);
  background:color-mix(in hsl, var(--panel) 92%, #000 6%); color:var(--text); cursor:pointer; transition:box-shadow .2s ease
}
.btn:hover,.btn-icon:hover{box-shadow:0 0 0 2px var(--ring)}
.btn-icon{width:38px; height:38px; padding:0}

/* Page layout */
main{padding:28px 0 56px}
h1,h2,h3{line-height:1.2}
h1{font-size:clamp(1.6rem,1.1rem + 1.6vw,2.2rem)}
h2{font-size:clamp(1.25rem,1rem + .8vw,1.6rem)}
h3{font-size:clamp(1.05rem,.95rem + .5vw,1.2rem)}
.hero{
  background:
    radial-gradient(1200px 400px at 30% -10%, color-mix(in hsl, var(--accent) 28%, transparent), transparent),
    radial-gradient(1200px 400px at 80% -10%, color-mix(in hsl, var(--accent2) 28%, transparent), transparent);
  border-bottom:1px solid var(--border)
}

/* Cards & grids */
.card{
  background:var(--panel); border:1px solid var(--border);
  border-radius:16px; padding:18px; box-shadow:0 10px 30px rgba(0,0,0,.35);
}
.grid{display:grid; gap:16px; grid-template-columns:repeat(auto-fit,minmax(260px,1fr));}

/* Text bits */
blockquote{border-left:4px solid var(--accent2); padding-left:12px; color:var(--muted)}
.audio-note{font-size:.9rem; color:var(--muted)}
hr{border:0; border-top:1px solid color-mix(in hsl, var(--border) 92%, #000 8%); margin:24px 0}

/* Media */
figure{margin:0; padding:0}
figcaption{font-size:.9rem; color:var(--muted); margin-top:6px}
audio{width:100%; margin:6px 0 12px}

/* Tables (responsive) */
.table-wrap{overflow:auto; border:1px solid var(--border); border-radius:12px}
.table{width:100%; border-collapse:collapse}
.table th,.table td{border-bottom:1px solid var(--border); padding:10px 12px; text-align:left}
.table th{background:color-mix(in hsl, var(--panel) 88%, #000 8%)}

/* Code blocks */
code{background:color-mix(in hsl, var(--panel) 88%, #000 8%); border:1px solid var(--border); padding:2px 6px; border-radius:6px}
pre{background:color-mix(in hsl, var(--panel) 92%, #000 8%); border:1px solid var(--border); padding:12px; border-radius:12px; overflow:auto}

/* Quiz */
.quiz{background:color-mix(in hsl, var(--panel) 92%, #000 8%); border:1px solid var(--border); border-radius:16px; padding:16px}
.quiz p{margin:10px 0 6px; font-weight:600}
.quiz label{display:inline-block; padding:6px 10px; border-radius:8px; cursor:pointer; margin:2px 0 6px}
.quiz input[type="radio"]{margin-right:6px}
.quiz label.correct{background:rgba(46,204,113,.18); outline:1px solid rgba(46,204,113,.6)}
.quiz label.incorrect{background:rgba(231,76,60,.18); outline:1px solid rgba(231,76,60,.6)}
.quiz label.quiz-correct-answer{box-shadow:inset 0 0 0 2px rgba(66,197,138,.35)}
#quiz-result{padding:10px 12px; border-radius:8px; background:#0e1730; border:1px solid #24335a; display:inline-block; margin-top:10px}

/* Notice */
.notice{background:color-mix(in hsl, var(--accent2) 18%, transparent); border:1px solid color-mix(in hsl, var(--accent2) 40%, transparent); color:var(--text); padding:10px 12px; border-radius:12px}

/* TOC links */
.toc a{display:block; padding:6px 10px; border-radius:10px; color:var(--muted); text-decoration:none}
.toc a:hover{background:color-mix(in hsl, var(--panel) 88%, #000 8%); color:var(--text)}

/* Modern citations (chip style) */
.cite{
  font-size:.85em; vertical-align:super; text-decoration:none; margin-left:2px; padding:0 6px;
  border-radius:999px; background:var(--chip); color:var(--chipText); border:1px solid var(--border)
}
.cite:hover{box-shadow:0 0 0 2px var(--ring)}
.cite[data-cite]:hover::after{
  content:attr(data-cite); position:absolute; transform:translateY(-1.8rem);
  background:color-mix(in hsl, var(--panel) 92%, #000 6%); border:1px solid var(--border); padding:6px 8px; border-radius:8px; white-space:nowrap;
  color:var(--text); box-shadow:0 6px 20px rgba(0,0,0,.35)
}
/* highlight target in bibliography */
.ref-highlight{animation:refPulse 1.6s ease 1; box-shadow:0 0 0 2px var(--accent2); border-radius:10px}
@keyframes refPulse{0%{background:rgba(61,210,195,.18)}100%{background:transparent}}

/* Back link under each bibliography entry */
.backref{
  font-size:.85rem;
  margin-left:6px;
  color:var(--muted);
}
.backref:hover{ color:var(--text); text-decoration:underline; }

/* Accessibility helpers */
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}

/* Footer */
footer{border-top:1px solid var(--border); color:var(--muted); padding:24px 0; font-size:.9rem}

/* Small-screen polish */
@media (max-width:640px){
  .nav{gap:8px}
  .card{padding:14px}
}