opensource category images should render correctly in dark mode

[jpvajda]

when viewing the OSS category images in repos on github or in on the OSS site in dark mode, the images don't render well in dark mode.

Examples

• nr1-github
• oss site category page

screen shots

Acceptance Criteria

• [ ] in dark mode OSS category images render correctly on Github and on the OSS Site.
• [ ] Don't break any existing image references to these category images as they are used in 100s of repos and are referenced into our repo templates and repo-linter checks.

[brammerl]

I'm going to try and work on this :)

[jpvajda]

i think this is unblocked now as the pr seems to have been merged.

[jpvajda]

I think this pr is also related https://github.com/newrelic/opensource-website/pull/816

[jpvajda]

I merged in #816. so closing