Implements T64929: Top right of 3D View looks crowded:
This code simply changes the layout of the navigation gizmo icons from horizontal to vertical, and it lightens the default theme color of the 3D view header. Also, the hard-coded tint of the icons was balanced to counteract the lightening of the header color. These changes are meant to deal with the crowded look in the top right of the viewport (See the task).
Here's a screenshot: