style.css

/* --- CSS Custom Properties (Light Theme - Default) --- */
:root {
  --bg-primary: #f6f8fa;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f6f8fa;
  --text-primary: #24292e;
  --text-secondary: #6a737d;
  --text-muted: #959da5;
  --border-color: #e1e4e8;
  --border-light: #eaecef;
  --divider-color: #d1d5da;
  --divider-active: #0366d6;
  --link-color: #0366d6;
  --code-bg: rgba(27, 31, 35, 0.05);
  --pre-bg: #f6f8fa;
  --pre-border: #e1e4e8;
  --blockquote-border: #dfe2e5;
  --table-header-bg: #f6f8fa;
  --table-row-alt: #f6f8fa;
  --table-border: #dfe2e5;
  --error-bg: #ffeef0;
  --error-border: #fdaeb7;
  --error-text: #cb2431;
  --mermaid-bg: #ffffff;
}

/* --- Dark Theme --- */
[data-theme="dark"] {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #21262d;
  --text-primary: #c9d1d9;
  --text-secondary: #8b949e;
  --text-muted: #6e7681;
  --border-color: #30363d;
  --border-light: #21262d;
  --divider-color: #30363d;
  --divider-active: #58a6ff;
  --link-color: #58a6ff;
  --code-bg: rgba(110, 118, 129, 0.2);
  --pre-bg: #161b22;
  --pre-border: #30363d;
  --blockquote-border: #3b434b;
  --table-header-bg: #161b22;
  --table-row-alt: #161b22;
  --table-border: #30363d;
  --error-bg: #3d1f28;
  --error-border: #f85149;
  --error-text: #f85149;
  --mermaid-bg: #161b22;
}

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

html, body {
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    Oxygen, Ubuntu, Cantarell, "Helvetica Neue", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  transition: background-color 0.2s ease, color 0.2s ease;
}

/* --- Toolbar (Theme Toggle + Share) --- */
.toolbar {
  position: fixed;
  top: 12px;
  right: 12px;
  z-index: 100;
  display: flex;
  gap: 8px;
}

.toolbar-btn {
  width: 40px;
  height: 40px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  background-color: var(--bg-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  transition: background-color 0.2s ease, border-color 0.2s ease;
}

.toolbar-btn:hover {
  background-color: var(--bg-tertiary);
}

.toolbar-btn .icon-moon {
  display: none;
}

[data-theme="dark"] .toolbar-btn .icon-sun {
  display: none;
}

[data-theme="dark"] .toolbar-btn .icon-moon {
  display: inline;
}

/* --- Share Toast Notification --- */
.share-toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background-color: var(--text-primary);
  color: var(--bg-secondary);
  padding: 10px 20px;
  border-radius: 8px;
  font-size: 14px;
  opacity: 0;
  transition: transform 0.3s ease, opacity 0.3s ease;
  z-index: 200;
  pointer-events: none;
}

.share-toast.visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* --- Main Split-Pane Layout --- */
main {
  display: flex;
  flex-direction: row;
  height: 100vh;
  overflow: hidden;
}

/* --- Editor Section --- */
.editor-section {
  flex: 1 1 50%;
  min-width: 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

#editor {
  width: 100%;
  height: 100%;
  padding: 16px 20px;
  border: none;
  outline: none;
  resize: none;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo,
    Courier, monospace;
  font-size: 14px;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-secondary);
  tab-size: 4;
  transition: background-color 0.2s ease, color 0.2s ease;
}

#editor::placeholder {
  color: var(--text-muted);
  font-style: italic;
}

#editor.drag-over {
  outline: 2px dashed var(--divider-active);
  outline-offset: -4px;
  background-color: var(--bg-tertiary);
}

/* --- Resizable Divider --- */
.divider {
  flex: 0 0 6px;
  background-color: var(--divider-color);
  cursor: col-resize;
  cursor: grab;
  position: relative;
  transition: background-color 0.15s ease;
  z-index: 10;
}

.divider:hover,
.divider:active {
  background-color: var(--divider-active);
}

.divider:active {
  cursor: grabbing;
}

/* --- Preview Section --- */
.preview-section {
  flex: 1 1 50%;
  min-width: 0;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background-color: var(--bg-secondary);
  transition: background-color 0.2s ease;
}

.preview-panel {
  width: 100%;
  height: 100%;
  padding: 24px 32px;
  overflow-y: auto;
  word-wrap: break-word;
  overflow-wrap: break-word;
}

/* --- Placeholder for Empty Preview --- */
.preview-panel:empty::before {
  content: "Start typing Markdown to see a live preview...";
  color: var(--text-muted);
  font-style: italic;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
}

.preview-panel .placeholder {
  color: var(--text-muted);
  font-style: italic;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
  user-select: none;
}


/* ============================================
   Rendered Markdown Element Styles
   ============================================ */

/* --- Headings --- */
.preview-panel h1,
.preview-panel h2,
.preview-panel h3,
.preview-panel h4,
.preview-panel h5,
.preview-panel h6 {
  margin-top: 24px;
  margin-bottom: 16px;
  font-weight: 600;
  line-height: 1.25;
}

.preview-panel h1 {
  font-size: 2em;
  padding-bottom: 0.3em;
  border-bottom: 1px solid var(--border-light);
}

.preview-panel h2 {
  font-size: 1.5em;
  padding-bottom: 0.3em;
  border-bottom: 1px solid var(--border-light);
}

.preview-panel h3 {
  font-size: 1.25em;
}

.preview-panel h4 {
  font-size: 1em;
}

.preview-panel h5 {
  font-size: 0.875em;
}

.preview-panel h6 {
  font-size: 0.85em;
  color: var(--text-secondary);
}

.preview-panel h1:first-child,
.preview-panel h2:first-child,
.preview-panel h3:first-child {
  margin-top: 0;
}

/* --- Paragraphs --- */
.preview-panel p {
  margin-top: 0;
  margin-bottom: 16px;
}

/* --- Links --- */
.preview-panel a {
  color: var(--link-color);
  text-decoration: none;
}

.preview-panel a:hover {
  text-decoration: underline;
}

/* --- Bold & Italic --- */
.preview-panel strong {
  font-weight: 600;
}

.preview-panel em {
  font-style: italic;
}

/* --- Strikethrough (GFM) --- */
.preview-panel del {
  text-decoration: line-through;
  color: var(--text-secondary);
}

/* --- Blockquotes --- */
.preview-panel blockquote {
  margin: 0 0 16px 0;
  padding: 0 16px;
  color: var(--text-secondary);
  border-left: 4px solid var(--blockquote-border);
}

.preview-panel blockquote > :first-child {
  margin-top: 0;
}

.preview-panel blockquote > :last-child {
  margin-bottom: 0;
}

/* --- Lists --- */
.preview-panel ul,
.preview-panel ol {
  margin-top: 0;
  margin-bottom: 16px;
  padding-left: 2em;
}

.preview-panel li {
  margin-bottom: 4px;
}

.preview-panel li > p {
  margin-bottom: 8px;
}

.preview-panel ul ul,
.preview-panel ul ol,
.preview-panel ol ul,
.preview-panel ol ol {
  margin-top: 0;
  margin-bottom: 0;
}

/* --- Task Lists (GFM) --- */
.preview-panel ul.contains-task-list,
.preview-panel .task-list-item {
  list-style-type: none;
}

.preview-panel ul.contains-task-list {
  padding-left: 0;
}

.preview-panel .task-list-item {
  position: relative;
  padding-left: 1.6em;
}

.preview-panel .task-list-item input[type="checkbox"] {
  position: absolute;
  left: 0;
  top: 0.3em;
  margin: 0;
  cursor: pointer;
}

/* --- Tables (GFM) --- */
.preview-panel table {
  width: 100%;
  border-collapse: collapse;
  border-spacing: 0;
  margin-top: 0;
  margin-bottom: 16px;
  overflow: auto;
  display: block;
}

.preview-panel table th,
.preview-panel table td {
  padding: 6px 13px;
  border: 1px solid var(--table-border);
}

.preview-panel table th {
  font-weight: 600;
  background-color: var(--table-header-bg);
}

.preview-panel table tr {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
}

.preview-panel table tr:nth-child(2n) {
  background-color: var(--table-row-alt);
}

/* --- Code: Inline --- */
.preview-panel code {
  padding: 0.2em 0.4em;
  margin: 0;
  font-size: 85%;
  background-color: var(--code-bg);
  border-radius: 3px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo,
    Courier, monospace;
}

/* --- Code Blocks (with highlight.js integration) --- */
.preview-panel pre {
  margin-top: 0;
  margin-bottom: 16px;
  padding: 16px;
  overflow: auto;
  font-size: 85%;
  line-height: 1.45;
  background-color: var(--pre-bg);
  border-radius: 6px;
  border: 1px solid var(--pre-border);
}

.preview-panel pre code {
  display: block;
  padding: 0;
  margin: 0;
  overflow: visible;
  font-size: 100%;
  line-height: inherit;
  word-wrap: normal;
  background-color: transparent;
  border: 0;
  border-radius: 0;
}

/* Ensure highlight.js theme integrates cleanly */
.preview-panel pre code.hljs {
  padding: 0;
  background: transparent;
}

/* --- Copy Button on Code Blocks --- */
.preview-panel pre .copy-btn {
  position: absolute;
  top: 8px;
  right: 8px;
  padding: 4px;
  font-size: 12px;
  font-family: inherit;
  color: var(--text-secondary);
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.15s ease, background-color 0.15s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
}

.preview-panel pre:hover .copy-btn {
  opacity: 1;
}

.preview-panel pre .copy-btn:hover {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

/* --- Images --- */
.preview-panel img {
  max-width: 100%;
  height: auto;
  border-radius: 4px;
  display: block;
  margin: 8px 0;
}

/* Broken image styling */
.preview-panel img.broken-image {
  border: 1px dashed var(--border-color);
  padding: 8px;
  color: var(--text-secondary);
  font-style: italic;
  min-height: 40px;
}

/* --- Horizontal Rules --- */
.preview-panel hr {
  height: 0.25em;
  padding: 0;
  margin: 24px 0;
  background-color: var(--border-color);
  border: 0;
}

/* --- Mermaid Diagrams --- */
.preview-panel pre.mermaid {
  background-color: var(--mermaid-bg);
  border: 1px solid var(--border-color);
  text-align: center;
  padding: 16px;
}

.preview-panel .mermaid-error {
  color: var(--error-text);
  background-color: var(--error-bg);
  border: 1px solid var(--error-border);
  border-radius: 6px;
  padding: 12px 16px;
  font-size: 0.875rem;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo,
    Courier, monospace;
  white-space: pre-wrap;
  margin-bottom: 16px;
}

/* ============================================
   Responsive Layout
   ============================================ */
@media (max-width: 767px) {
  main {
    flex-direction: column;
  }

  .editor-section {
    flex: 0 0 45%;
    min-height: 200px;
  }

  .divider {
    flex: 0 0 6px;
    cursor: row-resize;
    cursor: grab;
  }

  .preview-section {
    flex: 1 1 auto;
    min-height: 200px;
  }

  .preview-panel {
    padding: 16px;
  }
}

/* --- Utility: Prevent text selection during divider drag --- */
body.resizing {
  user-select: none;
  -webkit-user-select: none;
  cursor: col-resize;
}

@media (max-width: 767px) {
  body.resizing {
    cursor: row-resize;
  }
}