Chroma: Add vs theme to mainframe

[nginx-jack]

Add vs theme to mainframe.

This is not the final code block style, but an initial pass with the default vs theme values.

This removes the custom render-codeblock as it generated html and class references that would not work with the standard chroma theme generator. We may create another render-codeblock in future, if we require a fully custom theme to render our "fancy codeblocks".

Proposed changes

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• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
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