Fix ForumWidget not visible in dark theme

[kyrers]

Fixes #114.

For comparison, the following images show the behavior in light and dark mode respectively, with these changes.

[vercel[bot]]

@kyrers is attempting to deploy a commit to the Flashbots Team on Vercel.

A member of the Team first needs to authorize it.

[deadpine]

Fixed on https://github.com/flashbots/flashbots-writings-website/pull/133