consistent CSS spacing

Ensure consistent spacing across UI components by using CSS custom properties for padding/margins and applying spacing only when elements exist. This prevents visual inconsistencies between different UI states and modes.

Use CSS custom properties for consistent spacing values:

#TabsToolbar {
  padding: var(--zen-toolbox-padding);
}

Apply spacing conditionally using CSS selectors to prevent unnecessary gaps:

/* Only apply margin when pinned tabs exist */
#vertical-pinned-tabs-container:has(tab:not([hidden])) {
  margin-bottom: 8px;
}

This approach ensures that spacing remains consistent across different modes while preventing alignment issues when certain elements are not present.