:root {
  --bg: #ffffff;
  --bg-elev: #f5f5f7;
  --bg-code: #f0f0f3;
  --fg: #1b1b1f;
  --fg-muted: #57575c;
  --border: #d8d8dd;
  --accent: #2563eb;
  --accent-fg: #ffffff;
  --blockquote: #6b6b70;
}

[data-theme="dark"] {
  --bg: #111214;
  --bg-elev: #1a1b1e;
  --bg-code: #232428;
  --fg: #e8e8ea;
  --fg-muted: #9a9aa0;
  --border: #2a2b2f;
  --accent: #60a5fa;
  --accent-fg: #0b0c0e;
  --blockquote: #9a9aa0;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  transition: background 0.15s ease, color 0.15s ease;
}

body.pdf-exporting, body.pdf-exporting * {
  transition: none !important;
}

body {
  display: flex;
  flex-direction: column;
}

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 20px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-elev);
}

header h1 {
  margin: 0;
  font-size: 16px;
  font-weight: 600;
  letter-spacing: 0.01em;
}

.controls {
  display: flex;
  gap: 8px;
}

.controls button {
  background: var(--bg);
  color: var(--fg);
  border: 1px solid var(--border);
  padding: 6px 12px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
  font-family: inherit;
  transition: background 0.12s ease, border-color 0.12s ease;
}

.controls button:hover {
  border-color: var(--accent);
}

#theme-btn {
  min-width: 36px;
  padding: 6px 8px;
}

main {
  flex: 1;
  display: grid;
  grid-template-columns: 1fr 1fr;
  min-height: 0;
}

.pane {
  display: flex;
  flex-direction: column;
  min-height: 0;
  border-right: 1px solid var(--border);
}

.pane:last-child { border-right: none; }

.pane-header {
  padding: 8px 16px;
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--fg-muted);
  border-bottom: 1px solid var(--border);
  background: var(--bg-elev);
}

#editor {
  flex: 1;
  width: 100%;
  padding: 16px 20px;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 14px;
  line-height: 1.55;
  border: none;
  resize: none;
  outline: none;
  background: var(--bg);
  color: var(--fg);
  tab-size: 2;
}

#preview {
  flex: 1;
  overflow-y: auto;
  padding: 16px 24px;
  line-height: 1.6;
}

#preview h1, #preview h2, #preview h3,
#preview h4, #preview h5, #preview h6 {
  margin-top: 1.2em;
  margin-bottom: 0.5em;
  line-height: 1.25;
}

#preview h1 { font-size: 1.9em; border-bottom: 1px solid var(--border); padding-bottom: 0.3em; }
#preview h2 { font-size: 1.5em; border-bottom: 1px solid var(--border); padding-bottom: 0.3em; }
#preview h3 { font-size: 1.2em; }

#preview p { margin: 0.8em 0; }

#preview a { color: var(--accent); text-decoration: none; }
#preview a:hover { text-decoration: underline; }

#preview code {
  background: var(--bg-code);
  padding: 0.15em 0.4em;
  border-radius: 4px;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.9em;
}

#preview pre {
  background: var(--bg-code);
  padding: 14px 16px;
  border-radius: 6px;
  overflow-x: auto;
}

#preview pre code {
  background: transparent;
  padding: 0;
  font-size: 0.88em;
}

#preview blockquote {
  border-left: 3px solid var(--border);
  margin: 1em 0;
  padding: 0.2em 1em;
  color: var(--blockquote);
}

#preview ul, #preview ol { padding-left: 1.6em; }
#preview li { margin: 0.25em 0; }

#preview table {
  border-collapse: collapse;
  margin: 1em 0;
}

#preview th, #preview td {
  border: 1px solid var(--border);
  padding: 6px 12px;
}

#preview th { background: var(--bg-elev); }

#preview img { max-width: 100%; height: auto; }

#preview hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 1.5em 0;
}

#preview .mermaid {
  margin: 1em 0;
  text-align: center;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px;
  overflow-x: auto;
}

#preview .mermaid svg { max-width: 100%; height: auto; }

#preview .mermaid.mermaid-error {
  text-align: left;
  color: #dc2626;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.88em;
  white-space: pre-wrap;
}

@media (max-width: 720px) {
  main { grid-template-columns: 1fr; grid-template-rows: 1fr 1fr; }
  .pane { border-right: none; border-bottom: 1px solid var(--border); }
  .pane:last-child { border-bottom: none; }
}