/* ============================================
   COLOR SCHEME & TYPOGRAPHY
   ============================================ */

:root {
  /* Dark Mode Color Palette */
  --bg-primary: #0f1419;
  --bg-secondary: #1a1f2e;
  --bg-tertiary: #252d3d;
  
  --text-primary: #e8ecf1;
  --text-secondary: #a0a9b8;
  --text-muted: #6b7280;
  
  --border-color: #2d3748;
  --border-light: #3f4754;
  
  --accent-primary: #58a6ff;
  --accent-hover: #79c0ff;
  --accent-danger: #f85149;
  --accent-success: #3fb950;
  
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 8px 20px rgba(0, 0, 0, 0.4);
  
  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", sans-serif;
  --font-mono: "Fira Code", "Consolas", "Monaco", monospace;
  --line-height-relaxed: 1.75;
  --line-height-tight: 1.5;
}

/* ============================================
   GLOBAL STYLES
   ============================================ */

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
}

body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  line-height: var(--line-height-relaxed);
  font-size: 15px;
}

/* ============================================
   APP CONTAINER & LAYOUT
   ============================================ */

.app {
  display: flex;
  flex-direction: column;
  height: 100vh;
  background-color: var(--bg-primary);
}

.app-header {
  padding: 2rem 1.5rem 1.5rem;
  background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-tertiary) 100%);
  border-bottom: 1px solid var(--border-light);
  text-align: center;
}

.app-title {
  margin: 0 0 0.5rem;
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

.app-subtitle {
  margin: 0;
  font-size: 0.95rem;
  color: var(--text-secondary);
  font-weight: 400;
}

/* ============================================
   TOOLBAR
   ============================================ */

.formatting-toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  padding: 1rem 1.5rem;
  background-color: var(--bg-secondary);
  border-bottom: 1px solid var(--border-light);
  align-items: center;
}

.toolbar-group {
  display: flex;
  gap: 0.5rem;
  padding-bottom: 0;
}

.toolbar-group:not(:last-child)::after {
  content: "";
  width: 1px;
  height: 24px;
  background-color: var(--border-light);
  margin-left: 0.25rem;
}

.toolbar-actions {
  margin-left: auto;
  border: none;
}

.toolbar-actions::after {
  display: none !important;
}

.toolbar-btn {
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  white-space: nowrap;
  min-width: 36px;
}

.toolbar-btn:hover {
  background-color: var(--bg-primary);
  border-color: var(--accent-primary);
  color: var(--accent-hover);
  box-shadow: var(--shadow-sm);
}

.toolbar-btn:active {
  transform: scale(0.95);
}

.toolbar-btn.secondary {
  background-color: transparent;
  border-color: var(--border-color);
  color: var(--text-secondary);
}

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

.toolbar-btn.danger:hover {
  border-color: var(--accent-danger);
  color: var(--accent-danger);
}

/* ============================================
   STATUS MESSAGE
   ============================================ */

.status-message {
  min-height: 28px;
  padding: 0.5rem 1.5rem;
  background-color: var(--bg-secondary);
  color: var(--text-secondary);
  font-size: 0.9rem;
  opacity: 0;
  transition: opacity 0.3s ease;
  text-align: center;
}

.status-message.show {
  opacity: 1;
}

.status-message.success {
  color: var(--accent-success);
}

.status-message.error {
  color: var(--accent-danger);
}

/* ============================================
   EDITOR & PREVIEW LAYOUT
   ============================================ */

.editor-preview-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0;
  flex: 1;
  overflow: hidden;
}

.editor-panel,
.preview-panel {
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border-light);
  background-color: var(--bg-secondary);
}

.editor-panel {
  border-right: 1px solid var(--border-light);
}

.panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border-light);
  background-color: var(--bg-tertiary);
}

.panel-header h2 {
  margin: 0;
  font-size: 1.1rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  color: var(--text-primary);
}

.close-preview {
  display: none;
  background: none;
  border: none;
  color: var(--text-secondary);
  font-size: 1.5rem;
  cursor: pointer;
  padding: 0;
  width: 28px;
  height: 28px;
  align-items: center;
  justify-content: center;
  border-radius: 4px;
  transition: all 0.2s ease;
}

.close-preview:hover {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
}

/* ============================================
   TEXTAREA
   ============================================ */

#editor {
  flex: 1;
  padding: 1.5rem;
  border: none;
  border-radius: 0;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 0.95rem;
  line-height: var(--line-height-tight);
  resize: none;
  outline: none;
  caret-color: var(--accent-primary);
}

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

#editor::selection {
  background-color: rgba(88, 166, 255, 0.2);
}

/* ============================================
   PREVIEW CONTENT
   ============================================ */

.preview-panel {
  overflow: hidden;
}

.preview-content {
  flex: 1;
  overflow-y: auto;
  padding: 1.5rem;
  word-wrap: break-word;
  overflow-wrap: break-word;
}

/* Preview Markdown Styling */

.preview-content h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-top: 1.5em;
  margin-bottom: 0.5em;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 0.3em;
}

.preview-content h2 {
  font-size: 1.6rem;
  font-weight: 700;
  margin-top: 1.2em;
  margin-bottom: 0.4em;
  letter-spacing: -0.01em;
  color: var(--text-primary);
}

.preview-content h3 {
  font-size: 1.35rem;
  font-weight: 600;
  margin-top: 1em;
  margin-bottom: 0.3em;
  color: var(--text-primary);
}

.preview-content h4 {
  font-size: 1.1rem;
  font-weight: 600;
  margin-top: 0.8em;
  margin-bottom: 0.2em;
  color: var(--text-primary);
}

.preview-content h5,
.preview-content h6 {
  font-size: 1rem;
  font-weight: 600;
  margin-top: 0.8em;
  margin-bottom: 0.2em;
  color: var(--text-secondary);
}

.preview-content p {
  margin: 1em 0;
  line-height: var(--line-height-relaxed);
}

.preview-content ul,
.preview-content ol {
  margin: 1em 0;
  padding-left: 2rem;
  line-height: var(--line-height-relaxed);
}

.preview-content li {
  margin: 0.5em 0;
}

.preview-content code {
  background-color: var(--bg-tertiary);
  color: var(--accent-primary);
  padding: 0.2em 0.5em;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.9em;
}

.preview-content pre {
  background-color: var(--bg-tertiary);
  border: 1px solid var(--border-light);
  border-radius: 8px;
  padding: 1rem;
  overflow-x: auto;
  margin: 1em 0;
  line-height: var(--line-height-tight);
}

.preview-content pre code {
  background-color: transparent;
  color: inherit;
  padding: 0;
  border-radius: 0;
  font-size: 0.9rem;
}

.preview-content blockquote {
  border-left: 3px solid var(--accent-primary);
  margin: 1em 0;
  padding: 0.5em 0 0.5em 1rem;
  color: var(--text-secondary);
  font-style: italic;
  background-color: rgba(88, 166, 255, 0.05);
  border-radius: 0 4px 4px 0;
}

.preview-content a {
  color: var(--accent-primary);
  text-decoration: none;
  border-bottom: 1px dotted var(--accent-primary);
  transition: all 0.2s ease;
}

.preview-content a:hover {
  color: var(--accent-hover);
  border-bottom-style: solid;
}

.preview-content table {
  border-collapse: collapse;
  width: 100%;
  margin: 1em 0;
  border: 1px solid var(--border-light);
  border-radius: 6px;
  overflow: hidden;
}

.preview-content th {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
  padding: 0.75rem;
  text-align: left;
  font-weight: 600;
  border-bottom: 2px solid var(--border-light);
}

.preview-content td {
  padding: 0.75rem;
  border-bottom: 1px solid var(--border-light);
}

.preview-content tr:hover {
  background-color: var(--bg-tertiary);
}

.preview-content hr {
  border: none;
  height: 2px;
  background: linear-gradient(to right, transparent, var(--border-light), transparent);
  margin: 2em 0;
}

/* GitHub Flavored Markdown - Task Lists */
.preview-content input[type="checkbox"] {
  margin-right: 0.5em;
  cursor: pointer;
}

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

/* ============================================
   FULLSCREEN MODE
   ============================================ */

.app.fullscreen-preview {
  overflow: hidden;
}

.app.fullscreen-preview .app-header,
.app.fullscreen-preview .formatting-toolbar,
.app.fullscreen-preview .status-message,
.app.fullscreen-preview .editor-panel {
  display: none;
}

.app.fullscreen-preview .editor-preview-container {
  grid-template-columns: 1fr;
}

.app.fullscreen-preview .preview-panel {
  border: none;
}

.app.fullscreen-preview .close-preview {
  display: flex;
}

/* ============================================
   RESPONSIVE DESIGN
   ============================================ */

@media (max-width: 768px) {
  .editor-preview-container {
    grid-template-columns: 1fr;
  }

  .editor-panel {
    border-right: none;
    border-bottom: 1px solid var(--border-light);
  }

  .preview-panel {
    display: none;
  }

  .preview-panel.show {
    display: flex;
  }

  .formatting-toolbar {
    gap: 0.5rem;
    padding: 0.75rem;
  }

  .toolbar-btn {
    padding: 0.4rem 0.6rem;
    font-size: 0.85rem;
  }

  .app-title {
    font-size: 1.5rem;
  }

  .app-header {
    padding: 1.5rem 1rem 1rem;
  }

  #editor {
    padding: 1rem;
    font-size: 0.9rem;
  }

  .preview-content {
    padding: 1rem;
  }

  .preview-content h1 {
    font-size: 1.6rem;
  }

  .preview-content h2 {
    font-size: 1.3rem;
  }

  .preview-content h3 {
    font-size: 1.1rem;
  }
}