Pygments doesn't always recognize all syntax in a file, and while this

is often harmless, it comes with a lot of visual noise in the form of a

red border around the unexpected parts.
The indicator was more useful once upon a time, but with modern

practices around lint checking and CI builds, these markers are more

annoying than helpful.
This change removes visual indicators on unknown syntax, allowing

reviewers to concentrate more on the code without the distractions.

Posted a change with a LessCSS file that triggered Pygments error

markers. Saw that the change lacked the borders.