:root{
  --bg:#f6f8fb;
  --card:#ffffff;
  --text:#1f2937;
  --muted:#667085;
  --line:#dde3ec;
  --link:#1d4ed8;
}
*{box-sizing:border-box}
body{
  margin:0;
  font-family:Arial, Helvetica, sans-serif;
  background:var(--bg);
  color:var(--text);
  line-height:1.68;
}
.container{
  max-width:980px;
  margin:0 auto;
  padding:32px 20px 48px;
}
header{
  margin-bottom:20px;
}
h1{
  margin:0 0 8px;
  font-size:2rem;
}
h2{
  margin:28px 0 14px;
  font-size:1.35rem;
}
p{
  margin:14px 0;
}
.card{
  background:var(--card);
  border:1px solid var(--line);
  border-radius:16px;
  padding:22px 24px;
  margin:16px 0;
  box-shadow:0 6px 18px rgba(16,24,40,.05);
}
.nav{
  display:flex;
  flex-wrap:wrap;
  gap:10px;
  margin-top:18px;
}
.nav a, .back{
  display:inline-block;
  padding:8px 12px;
  border:1px solid var(--line);
  border-radius:999px;
  background:#fff;
  text-decoration:none;
  color:var(--link);
}
a{
  color:var(--link);
  text-decoration:none;
}
a:hover{
  text-decoration:underline;
}
.list{
  padding-left:22px;
}
.list li{
  margin:8px 0;
}
.muted{
  color:var(--muted);
}
.math-block{
  overflow-x:auto;
  padding:8px 0;
  margin:6px 0;
}
mjx-container{
  overflow-x:auto;
  overflow-y:hidden;
  max-width:100%;
}
code{
  background:#eef2f7;
  padding:2px 6px;
  border-radius:6px;
}