:root {
  --bg:       #0d1117;
  --sidebar:  #161b22;
  --border:   #30363d;
  --accent:   #58a6ff;
  --text:     #e6edf3;
  --muted:    #8b949e;
  --hover:    #1f2937;
  --active:   #1c2d3f;
  --code-bg:  #161b22;
}
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: 'Inter', sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  height: 100vh;
  overflow: hidden;
}

/* Activity Bar */
#activity-bar {
  width: 56px;
  background: #090c10;
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  align-items: center;
  padding-top: 16px;
  gap: 12px;
  flex-shrink: 0;
  z-index: 10;
}
.activity-item {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 6px;
  cursor: pointer;
  font-size: 20px;
  color: var(--muted);
  transition: all 0.15s;
  position: relative;
  opacity: 0.6;
}
.activity-item:hover { opacity: 1; background: var(--hover); }
.activity-item.active { opacity: 1; background: var(--hover); }
.activity-item.active::before {
  content: '';
  position: absolute;
  left: -10px;
  top: 6px;
  bottom: 6px;
  width: 3px;
  background: var(--accent);
  border-radius: 0 3px 3px 0;
}

/* ── Sidebar ── */
#sidebar {
  width: 250px;
  min-width: 200px;
  max-width: 360px;
  background: var(--sidebar);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  flex-shrink: 0;
}
#sidebar-header {
  padding: 18px 16px 12px;
}
#sidebar-header h1 {
  font-size: 11px;
  text-transform: uppercase;
  font-weight: 600;
  color: var(--muted);
  letter-spacing: 0.05em;
}

#search-wrap {
  padding: 0 12px 10px;
  border-bottom: 1px solid var(--border);
}
#search {
  width: 100%;
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 4px;
  padding: 6px 8px;
  font-size: 12px;
  outline: none;
  transition: border-color 0.2s;
}
#search:focus { border-color: var(--accent); }

#file-list {
  flex: 1;
  overflow-y: auto;
  padding: 8px 0;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

/* Tree Nodes */
.folder-item {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 10px;
  cursor: pointer;
  font-size: 13px;
  color: var(--text);
  font-weight: 500;
  user-select: none;
}
.folder-item:hover { background: var(--hover); }
.folder-icon {
  font-size: 12px;
}
.folder-icon::after { content: '📂'; }
.folder-item.collapsed .folder-icon::after { content: '📁'; }

.file-item {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 10px;
  cursor: pointer;
  font-size: 13px;
  color: var(--muted);
  user-select: none;
}
.file-item:hover { background: var(--hover); color: var(--text); }
.file-item.active { background: var(--active); color: var(--accent); }

.file-item.mastered .name {
  color: var(--muted);
  text-decoration: line-through;
  opacity: 0.5;
}

.file-item.mastered .icon {
  opacity: 1;
  filter: grayscale(0);
}

.file-item .icon { transition: transform 0.2s; }
.file-item:hover .icon { transform: scale(1.1); }

/* Sidebar Header & Search Refinement */
#search {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 6px 10px;
  border-radius: 6px;
  width: 100%;
  font-size: 13px;
  transition: border-color 0.2s;
}

#search:focus {
  border-color: var(--accent);
  outline: none;
}

#hide-mastered-btn:hover {
  background: var(--hover);
}

/* ── Sidebar Toggle ── */
#sidebar.collapsed { display: none !important; }
#sidebar-toggle {
  font-size: 20px;
  cursor: pointer;
  color: var(--muted);
  user-select: none;
  line-height: 1;
}
#sidebar-toggle:hover { color: var(--text); }

@media (max-width: 768px) {
  #sidebar {
    position: absolute;
    left: 56px;
    top: 53px;
    bottom: 0;
    z-index: 50;
    box-shadow: 4px 4px 12px rgba(0,0,0,0.5);
  }
  #content-wrap { padding: 20px 16px !important; }
}

/* ── Main ── */
#main {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background: var(--bg);
}
#topbar {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 24px;
  border-bottom: 1px solid var(--border);
  background: var(--sidebar);
  min-height: 52px;
}
#topbar-title {
  font-size: 13px;
  font-weight: 500;
  color: var(--text);
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
#loading-badge { display: none; font-size: 11px; color: var(--muted); }

#content-wrap {
  flex: 1;
  overflow-y: auto;
  padding: 36px 48px;
  scrollbar-width: thin;
}
#content { max-width: 800px; margin: 0 auto; }

/* Markdown styles */
#content h1 { font-size: 26px; font-weight: 700; border-bottom: 1px solid var(--border); padding-bottom: 10px; margin-bottom: 20px; color: var(--text); }
#content h2 { font-size: 19px; font-weight: 600; margin: 32px 0 12px; color: var(--text); }
#content h3 { font-size: 15px; font-weight: 600; margin: 24px 0 8px; color: #cdd9e5; }
#content p  { line-height: 1.75; margin-bottom: 14px; font-size: 14px; color: #cdd9e5; }
#content a  { color: var(--accent); text-decoration: none; }
#content a:hover { text-decoration: underline; }
#content ul, #content ol { padding-left: 22px; margin-bottom: 14px; }
#content li { line-height: 1.75; font-size: 14px; color: #cdd9e5; margin-bottom: 4px; }
#content strong { color: var(--text); font-weight: 600; }
#content em { color: #d2a634; }
#content blockquote { border-left: 3px solid var(--accent); padding: 8px 16px; margin: 16px 0; background: #1c2d3f55; border-radius: 0 6px 6px 0; color: #8b949e; font-size: 13.5px; }
#content code { font-family: 'JetBrains Mono', monospace; background: var(--code-bg); border: 1px solid var(--border); border-radius: 4px; padding: 1px 5px; font-size: 12.5px; color: #f85149; }
#content pre { background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px; padding: 18px 20px; overflow-x: auto; margin: 16px 0; }
#content pre code { background: none; border: none; padding: 0; color: #e6edf3; }
#content table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 13px; }
#content th { background: #1c2d3f; color: var(--accent); font-weight: 600; padding: 9px 14px; text-align: left; border: 1px solid var(--border); }
#content td { padding: 8px 14px; border: 1px solid var(--border); color: #cdd9e5; vertical-align: top; }
#content tr:nth-child(even) td { background: #ffffff06; }
#content hr { border: none; border-top: 1px solid var(--border); margin: 28px 0; }

#placeholder { display: flex; flex-direction: column; align-items: center; justify-content: center; height: 100%; color: var(--muted); gap: 12px; }
#placeholder .icon { font-size: 48px; }