[Wiki] Sidebar: Create guidance for sidebar styling in dark mode (borders, surfaces)

This issue represents a finding from our work to audit features belonging to groupknowledge. See the analysis in Figma for more information.

[Wiki] Draggable Sidebar Border Styling Update

Background

The wiki sidebar has a draggable border that currently uses hardcoded color values. We need to update these to use GitLab's design tokens for better consistency and dark mode support.

Current Implementation

The draggable border is currently defined in app/assets/stylesheets/framework/common.scss:

.drag-handle {
  width: 4px;
  &:hover {
    background-color: $gray-50;
  }
  &.is-dragging {
    background-color: $gray-400;
  }
}

Related Issues

Edited by James Rushford