Fix community solution summary background in dark mode

[homersimpsons]

The community solution summary does not display well in dark mode, here is a small fix for it: 💄 Fix community solution summary background in dark mode by homersimpsons · Pull Request #5371 · exercism/website · GitHub

Before:

After:

[iHiD]

Thanks! (cc @dem4ron)

[dem4ron]

Thanks for noticing, it is fixed now!