Fix sidebar collapse icon color

Created by: oleggromov

There was a minor regression with the color of the expand/collapse icon in the sidebar.

This PR addresses the issue.

Design

As per our design system, the icon should be --body-color to match the designs in both light and dark modes.

In Design System

Light	Dark

After the Change

Light	Dark

Test plan

1. pull the branch
2. run the app
3. ensure that colors match

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.