The QuickLook render plugin for ReST supports syntax highlight in code blocks. If the specified language is supported by Nim's highlite module they will be rendered statically in Nim, generating plain HTML+CSS. Unsupported languages will use the Prism syntax highlighter. This increases the size of the generated HTML and may not be as precise as a proper syntax highlighter, but seems to work overall pretty well.
The list of languages supported natively by Nim is:
The list of supported languages through prism.js is: