fix: block code rendering with transparent background

[scottmckendry]

Hello @MeanderingProgrammer! 🙂

First off, congrats on v5.0.0! Lots of great new features to play with!

Here is the fix for the issue described in #73 observed when using a transparent background.

Before:

After:

This was due to passing in the hl_mode = 'combine' option.

From the docs:

hl_mode : control how highlights are combined with the highlights of the text. Currently only affects virt_text highlights, but might affect hl_group in later versions.

• "replace": only show the virt_text color. This is the default.
• "combine": combine with background text color.
• "blend": blend with background text color. Not supported for "inline" virt_text.

I've only tested this for a transparent background, but I'm 99% sure this will work the same way for solid backgrounds as well.

[MeanderingProgrammer]

Ah, that makes sense! Tested it with a solid background locally, it works.

Thanks for the PR!