Apply styling changes to the left sidebar

Proposal

With the work that is being done to consolidate the top nav #301143 (closed), we would be applying some new design styling inspired by explorations done by the UX Foundations team gitlab-design#1424 (closed).

This proposal extracts elements of the explorations that we are confident with moving forward with

• Reduce visual noise by changing active menu item state
• Better differentiate left nav from main body content (and improve accessibility) by updating background color
• Reduce visual noise by removing the right border from the left nav
• Create better color contrast and improve accessibility by changing left nav font color to indigo-900
• Enable full view of left nav without scrolling by removing extra bottom padding to sub-menu when expanded and reducing menu item top and bottom padding so that each menu item is 32px in height
• Improve color contrast by changing styling of the pills that indicate number of issues and merge requests

Current	Proposal

Project name area

• Align project name area with updated styling of left nav
  • Reduce height of project name area from 60px to 48px
  • Reduce size of project logo from 40px to 32px (Medium size aligned to Pajamas)
  • The active state has a 4px padding around product logo/title area

Design specifications

Figma [Specifications]: https://www.figma.com/file/SMs53NHLP7NJhlPOmnO7Ca/?node-id=1846%3A55175