/* Math base layout system (independent from Code) */

:root{
    --bg: #ffffff;
    --ink: #0f172a;
    --muted: rgba(15, 23, 42, 0.72);
    --border: rgba(15, 23, 42, 0.12);
    --card: #ffffff;
    --radius: 16px;
    --shadow: 0 8px 22px rgba(0,0,0,0.06);
  }
  
  *{ box-sizing: border-box; }
  body{
    margin: 0;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
    color: var(--ink);
    background: var(--bg);
  }
  
  a{ color: inherit; }
  
  .page{
    max-width: 1100px;
    margin: 0 auto;
    padding: 18px;
  }
  
  .layout{
    display: grid;
    grid-template-columns: 260px 1fr;
    gap: 16px;
  }
  
  @media (max-width: 900px){
    .layout{ grid-template-columns: 1fr; }
    .sidebar{ order: 2; }
  }
  
  .topbar{
    border-bottom: 1px solid var(--border);
    background: #fff;
  }
  
  .nav-shell{
    max-width: 1100px;
    margin: 0 auto;
    padding: 14px 18px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 14px;
  }
  
  .nav-brand a{
    text-decoration: none;
    font-weight: 700;
  }
  
  .nav-links{
    display: flex;
    gap: 12px;
  }
  .nav-links a{
    text-decoration: none;
    padding: 8px 10px;
    border-radius: 12px;
    border: 1px solid transparent;
  }
  .nav-links a:hover{
    border-color: var(--border);
  }
  
  .sidebar{
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 14px;
    background: var(--card);
    box-shadow: var(--shadow);
  }
  .sidebar-title{
    margin: 0 0 10px;
    font-size: 1.05rem;
  }
  .side-nav{
    display: flex;
    flex-direction: column;
    gap: 6px;
  }
  .side-link{
    text-decoration: none;
    padding: 8px 10px;
    border-radius: 12px;
    border: 1px solid transparent;
    color: var(--muted);
  }
  .side-link:hover{ border-color: var(--border); color: var(--ink); }
  a.active{ border-color: var(--border); color: var(--ink); }
  
  .hero{
    padding: 18px;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    background: var(--card);
    box-shadow: var(--shadow);
  }
  .lede{ color: var(--muted); max-width: 70ch; }
  
  .grid{
    margin-top: 14px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
    gap: 12px;
  }
  
  .card{
    display: block;
    padding: 14px;
    border-radius: var(--radius);
    border: 1px solid var(--border);
    background: var(--card);
    text-decoration: none;
    box-shadow: var(--shadow);
  }
  .card:hover{ transform: translateY(-1px); }
  
  .footer{
    margin-top: 22px;
    padding: 16px 18px;
    border-top: 1px solid var(--border);
    color: var(--muted);
  }
  
  .side-divider{
    border: none;
    border-top: 1px solid var(--border);
    margin: 12px 0;
  }
  
  .units-title{
    font-weight: 700;
    margin: 0 0 8px;
    opacity: 0.85;
  }
  
  .units-nav{
    display: flex;
    flex-direction: column;
    gap: 6px;
  }
  
  .unit-link{
    text-decoration: none;
    padding: 10px 12px;
    border-radius: 14px;
    border: 1px solid transparent;
    color: rgba(15,23,42,0.75);
  }
  
  .unit-link:hover{
    border-color: var(--border);
    color: var(--ink);
  }
  
  /* ===== Sticky Top Header (Math + Code style) ===== */
/* ===== Sticky, full-width header aligned with page grid ===== */
.site-header{
  position: sticky;
  top: 0;
  z-index: 1000;
  width: 100%;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
}

/* Constrain whatever nav_systems.js renders so it aligns with .page */
  .site-header [data-top-nav]{
    max-width: 1100px;     /* same as .page */
    margin: 0 auto;
    padding: 14px 18px;    /* match your .page padding feel */
  }

/* ===== Page Title Header (matches CODE vibes) ===== */
.page-header{
  margin: 0;
  padding: 18px 0 8px 0;
    }

    .page-header h1{
      margin: 0;
      font-size: 2rem;
      line-height: 1.15;
    }

    .page-header .lede{
      margin: 8px 0 0 0;
      opacity: .85;
      max-width: 70ch;
    }

main.page{
  padding-top: 0; /* usually fine */
}