/* ─── Reset & Base ─────────────────────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --header-height: 52px;
  --footer-height: 32px;
  --mobile-tabs-height: 42px;
  --border-color: #e2e8f0;
  --bg-surface: #f8fafc;
  --bg-header: #1e293b;
  --text-header: #f1f5f9;
  --text-muted: #64748b;
  --accent: #3b82f6;
  --accent-hover: #2563eb;
  --resizer-width: 6px;
  --font-mono: "JetBrains Mono", "Fira Code", Consolas, "Courier New", monospace;
  --radius: 6px;
}

html, body {
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
  font-size: 15px;
  background: var(--bg-surface);
  color: #1e293b;
  overflow: hidden;
}

/* ─── Header ───────────────────────────────────────────────────────────── */
.app-header {
  height: var(--header-height);
  background: var(--bg-header);
  display: flex;
  align-items: center;
  padding: 0 16px;
  gap: 12px;
  flex-shrink: 0;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}

.app-title {
  color: var(--text-header);
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.3px;
  white-space: nowrap;
}

.header-center {
  display: flex;
  align-items: center;
  gap: 8px;
  flex: 1;
  justify-content: center;
}

.theme-label {
  color: #94a3b8;
  font-size: 13px;
}

.theme-select {
  background: #334155;
  color: var(--text-header);
  border: 1px solid #475569;
  border-radius: var(--radius);
  padding: 4px 10px;
  font-size: 13px;
  cursor: pointer;
  outline: none;
  transition: border-color 0.15s;
}

.theme-select:focus {
  border-color: var(--accent);
}

.header-right {
  display: flex;
  align-items: center;
  gap: 8px;
}

/* ─── Buttons ──────────────────────────────────────────────────────────── */
.btn {
  border: none;
  border-radius: var(--radius);
  padding: 5px 12px;
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, opacity 0.15s;
  white-space: nowrap;
}

.btn-primary {
  background: var(--accent);
  color: white;
}
.btn-primary:hover { background: var(--accent-hover); }

.btn-secondary {
  background: #334155;
  color: #cbd5e1;
  border: 1px solid #475569;
}
.btn-secondary:hover { background: #475569; }

.btn-ghost {
  background: transparent;
  color: #94a3b8;
  border: 1px solid #475569;
}
.btn-ghost:hover { background: #334155; color: var(--text-header); }

.btn-lang {
  min-width: 38px;
  text-align: center;
  font-weight: 700;
}

/* Scroll sync toggle */
.scroll-sync-label {
  display: flex;
  align-items: center;
  gap: 4px;
  cursor: pointer;
  user-select: none;
}

.scroll-sync-label input[type="checkbox"] {
  width: 14px;
  height: 14px;
  accent-color: var(--accent);
  cursor: pointer;
}

.scroll-sync-text {
  color: #94a3b8;
  font-size: 16px;
  line-height: 1;
}

/* ─── Mobile Tabs ──────────────────────────────────────────────────────── */
.mobile-tabs {
  display: none;
  height: var(--mobile-tabs-height);
  background: #1e293b;
  border-top: 1px solid #334155;
}

.tab-btn {
  flex: 1;
  border: none;
  background: transparent;
  color: #94a3b8;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, color 0.15s;
}

.tab-btn.active {
  color: white;
  border-bottom: 2px solid var(--accent);
}

/* ─── Main Split ───────────────────────────────────────────────────────── */
.main-split {
  display: flex;
  height: calc(100vh - var(--header-height) - var(--footer-height));
  overflow: hidden;
}

/* ─── Pane ─────────────────────────────────────────────────────────────── */
.pane {
  display: flex;
  flex-direction: column;
  flex: 1 1 0;
  min-width: 0;
  overflow: hidden;
  background: white;
}

.editor-pane {
  border-right: 1px solid var(--border-color);
}

.pane-header {
  height: 34px;
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  padding: 0 14px;
  gap: 8px;
  flex-shrink: 0;
}

.pane-label {
  font-size: 12px;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.save-status {
  font-size: 11px;
  color: #10b981;
  margin-left: auto;
}

/* ─── Editor Textarea ──────────────────────────────────────────────────── */
.editor-textarea {
  flex: 1;
  resize: none;
  border: none;
  outline: none;
  padding: 16px 18px;
  font-family: var(--font-mono);
  font-size: 14px;
  line-height: 1.65;
  color: #1e293b;
  background: white;
  tab-size: 2;
  overflow: auto;
}

.editor-textarea::placeholder {
  color: #b0bec5;
}

/* ─── Preview Pane ─────────────────────────────────────────────────────── */
.preview-pane {
  overflow-y: auto;
}

#preview-content {
  min-height: 100%;
}

/* ─── Resizer ──────────────────────────────────────────────────────────── */
.resizer {
  width: var(--resizer-width);
  background: var(--border-color);
  cursor: col-resize;
  flex-shrink: 0;
  transition: background 0.15s;
  position: relative;
}

.resizer:hover, .resizer:active {
  background: var(--accent);
}

.resizer::before {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 2px;
  height: 32px;
  border-left: 1px solid #94a3b8;
  border-right: 1px solid #94a3b8;
}

/* ─── Footer ───────────────────────────────────────────────────────────── */
.app-footer {
  height: var(--footer-height);
  background: var(--bg-surface);
  border-top: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  padding: 0 16px;
  gap: 4px;
  flex-shrink: 0;
}

.stat {
  font-size: 12px;
  color: var(--text-muted);
}

.stat-sep {
  color: #cbd5e1;
  font-size: 12px;
}

/* ─── Responsive / Mobile ──────────────────────────────────────────────── */
@media (max-width: 640px) {
  .header-center {
    display: none;
  }

  .header-right .btn-secondary,
  .header-right .btn-ghost:not(.btn-lang) {
    display: none;
  }

  .scroll-sync-label {
    display: none;
  }

  .theme-label { display: none; }

  .mobile-tabs {
    display: flex;
  }

  .main-split {
    height: calc(100vh - var(--header-height) - var(--mobile-tabs-height) - var(--footer-height));
    position: relative;
  }

  .resizer {
    display: none;
  }

  .pane {
    position: absolute;
    inset: 0;
    display: none;
    flex: none;
    width: 100%;
    height: 100%;
  }

  .pane.active {
    display: flex;
  }

  .editor-pane {
    border-right: none;
  }
}

/* ─── Scrollbar styling ────────────────────────────────────────────────── */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}
::-webkit-scrollbar-track {
  background: transparent;
}
::-webkit-scrollbar-thumb {
  background: #cbd5e1;
  border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
  background: #94a3b8;
}