#app-header {
  display: flex;
  flex-direction: column;
  z-index: 100;
  background-color: var(--site-surface);
  border-bottom: 1px solid var(--site-border);
}

#main-ribbon {
  display: flex;
  align-items: center;
  padding: 0 16px;
  height: 44px;
  user-select: none;
}

#toolbar {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 0 8px;
  height: 44px;
  user-select: none;
}

.toolbar-left, .toolbar-center, .toolbar-right {
  display: flex;
  align-items: center;
  gap: 4px;
}

.toolbar-left {
  justify-content: flex-start;
}

.toolbar-center {
  justify-content: center;
}

.toolbar-right {
  justify-content: flex-end;
}

/* Menu Bar Items */
.menu-bar {
  display: flex;
  align-items: center;
  gap: 2px;
}

.menu-item {
  position: relative;
}

.menu-title {
  padding: 4px 8px;
  font-size: 12px;
  font-weight: 500;
  color: var(--site-text);
  border-radius: var(--site-radius);
  cursor: pointer;
  transition: background var(--transition);
}

.menu-title:hover {
  background-color: var(--site-surface-hover);
}

/* Dropdown Menu Popup */
.menu-dropdown {
  position: absolute;
  top: 100%;
  left: 0;
  margin-top: 4px;
  background: var(--site-surface);
  border: 1px solid var(--site-border);
  box-shadow: var(--site-shadow-lg);
  border-radius: var(--site-radius-lg);
  min-width: 180px;
  display: none;
  flex-direction: column;
  padding: 4px 0;
  z-index: 1000;
}

.menu-item.active .menu-dropdown {
  display: flex;
}

.menu-option {
  padding: 6px 14px;
  font-size: 12px;
  color: var(--site-text);
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  transition: background var(--transition);
}

.menu-option:hover {
  background-color: var(--site-surface-hover);
  color: var(--site-accent);
}

.menu-shortcut {
  font-size: 10px;
  color: var(--site-text-muted);
}

.menu-divider {
  height: 1px;
  background-color: var(--site-border-light);
  margin: 4px 0;
}

#diagram-title {
  background: transparent;
  border: 1px solid transparent;
  color: var(--site-text);
  font-weight: 600;
  font-size: 13px;
  padding: 4px 8px;
  border-radius: var(--site-radius);
  width: 160px;
  margin-left: 8px;
}

#diagram-title:hover {
  border-color: var(--site-border);
}

#diagram-title:focus {
  outline: none;
  border-color: var(--site-accent);
  background-color: var(--site-bg);
}

.icon-btn {
  background: transparent;
  border: 1px solid transparent;
  color: var(--site-text);
  width: 30px;
  height: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--site-radius);
  cursor: pointer;
  transition: all var(--transition);
}

.icon-btn:hover:not(:disabled) {
  background-color: var(--site-surface-hover);
}