How to make a background box around a fraction (“bbox”) with Katex?

[q2apro]

The bbox command is not supported in Katex, see https://katex.org/docs/support_table.html

bbox with MathJax renders \bbox[#e1ffc1,5px]{ \frac{1}{2} } like:

I have tried in Katex the alternative command:

\colorbox{#e1ffc1}{ \frac{1}{2} }

but it throws the error:

KaTeX parse error: Can't use function '\frac' in text mode at position 21: …rbox{#e1ffc1}{ \̲f̲r̲a̲c̲{1}{2} }

Likewise \fcolorbox does not work.

How to get the background box in Katex around a fraction to work?

Question was also posted at https://stackoverflow.com/q/63970532/1066234

[ronkok]

In LaTeX, \colorbox puts its contents into text mode. And KaTeX is a bit pickier about text mode than MathJax is.

You can still put math inside the box, but you have to explicitly shift it from text mode back into math mode with $…$ delimiters. So, to get your example working, try \colorbox{#e1ffc1}{$ \frac{1}{2} $}

[willymcallister]

With \colorbox the color specification appears to be hard coded. The allowable arguments are #hexcodes and standard HTML color names. Can you think of a way to make the color responsive to dark/light mode? Find attached some examples. The light mode looks fine, but the dark mode would benefit from a switch to a different background color. The gray background is #808080, the center of the gray scale.

[edemaine]

@willymcallister This should probably be a different discussion thread, but I'll answer here anyway: \htmlClass is probably what you're looking for. See https://katex.org/docs/supported.html#html