:root {
  --bg: #ffffff;
  --text: #111827;
  --muted: #6b7280;
  --border: #e5e7eb;
  --codebg: #0b1020;
  --codefg: #e5e7eb;

  --graybox: #f3f4f6;
  --checkpoint: #ecfdf5;
  --checkpoint-border: #10b981;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  line-height: 1.6;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 18px;
}

.site-header {
  border-bottom: 1px solid var(--border);
  padding: 42px 0 28px;
}

.kicker {
  color: var(--muted);
  font-size: 14px;
  margin: 0 0 10px;
}

.site-header h1 {
  margin: 0 0 12px;
  font-size: clamp(30px, 4vw, 44px);
  letter-spacing: -0.02em;
  line-height: 1.15;
}

.lede {
  margin: 0;
  color: #374151;
  font-size: 18px;
  max-width: 70ch;
}

.article {
  padding: 28px 0 40px;
}

h2 {
  margin: 34px 0 10px;
  font-size: 26px;
  letter-spacing: -0.01em;
}

h3 {
  margin: 18px 0 10px;
  font-size: 18px;
}

p { margin: 10px 0; }

ul {
  padding-left: 22px;
  margin: 10px 0 16px;
}

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 0.95em;
  background: #f9fafb;
  border: 1px solid var(--border);
  padding: 0.15em 0.35em;
  border-radius: 6px;
}

.divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 36px 0;
}

/* Callouts */
.callout {
  margin: 16px 0;
  padding: 14px 14px;
  border-radius: 12px;
  border: 1px solid var(--border);
}

.callout-title {
  font-weight: 700;
  margin-bottom: 8px;
}

.callout.gray {
  background: var(--graybox);
}

.callout.checkpoint {
  background: var(--checkpoint);
  border-color: #bbf7d0;
  border-left: 6px solid var(--checkpoint-border);
}

.tree {
  margin: 0;
  padding: 12px;
  background: #ffffff;
  border-radius: 10px;
  border: 1px dashed #d1d5db;
  overflow-x: auto;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  font-size: 13px;
  line-height: 1.45;
}

/* Code blocks */
.codeblock {
  margin: 14px 0 18px;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border);
}

.codehdr {
  padding: 10px 12px;
  font-weight: 700;
  font-size: 13px;
  color: #111827;
  background: #f9fafb;
  border-bottom: 1px solid var(--border);
}

.codeblock pre {
  margin: 0;
  padding: 14px 14px;
  background: var(--codebg);
  color: var(--codefg);
  overflow-x: auto;
}

.codeblock pre code {
  background: transparent;
  border: none;
  padding: 0;
  color: inherit;
  font-size: 13px;
  line-height: 1.6;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 24px 0 42px;
  color: var(--muted);
}