[EuiCodeBlock] Allow switching theme type

[chetanmajithiya]

theme props to <EuiCodeBlock />, to make it this part Dark or Light on any theme,
for example https://elastic.github.io/eui/#/layout/header in Dark theme section theme="dark"

(<EuiCodeBlock theme="dark" />)

https://github.com/elastic/eui/discussions/4378

[cchaos]

Thanks for the feature request @chetanmajithiya . Currently it's not as easy as it may sound because we of how our CSS is built. However, next year we will be switching from SASS to Emotion as a CSS in JS solution #3912 which will open up the opportunity to do this. It will take some time, though so I'll add to our long-term roadmap.

[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.

[chandlerprall]

@cchaos do you think this theme prop is something we'd want to support on all components as they are converted to emotion?

[cchaos]

Yeah I was going to comment and say that we won't be doing any manual reverse theme props on components. Instead the CSS-in-JS effort #3912 will allow wrapping components in different themes. Therefore, I'm going to close this specific issue out and say to those wanting this feature, to keep a track on that Meta issue.