Bug: at-mention autocomplete doesn't use theme colors

[ogi-m]

Steps to reproduce the behavior

1. Set a dark theme
2. Go to boards
3. Open a card and type "@" in the comment field
4. Note the colors are off

Expected behavior

The autocomplete should match the colors for the selected theme

Screenshots

Edition and Platform

• Edition: Mattermost plugin
• Version: v0.11
• Browser and OS: Chrome & Firefox

[hahmadia]

Asaad has volunteered to help me with this problem.

[ogi-m]

Tested and passed on v0.11, the popup now respects the theme.