Line highlighting in codeblocks has changed

[bforbis]

I have recently just upgraded mkdocs-techdocs-core from v1.2.3 -> v1.3.5 and have been testing on my documentation smoke test page and noticed a significant change in how codeblock highlighting is visualized using the hl_lines directive.

Version 1.2.3

Version ^1.3.3

I'm not sure if this was an intentional style change or is a bug, but the new way that line highlighting works is too subtle and easy to miss.

I've done some testing of versions in between and this seems to have been introduced in mkdocs-techdocs-core@v1.3.3, which bumped mkdocs-material to 9.4.14

Looking at the css of the .hll and .highlight CSS class, it looks like the background-color was updated:

Old: background-color: var(--md-code-hl-color)
New: background-color: var(--md-code-hl-color--light)

This seems to have been changed in mkdocs-material as reported in squidfunk/mkdocs-material#6017

[pwalleni]

Here too. Please fix. Thanks.