Is there a way to highlight the text?

[LevYas]

I tried to use general methods like these:

<mark>yellow</mark>
<mark style="background-color: lightblue">Marked text</mark>
==marked==
<span style="background-color: #FFFF00">Marked text</span>

yellow
Marked text
==marked==
Marked text

But none of it worked. Yellow highlighting by default is fine, but I also want to change colors.
Is it difficult to add such functionality? I can make a PR, but gonna need pointers on how to implement that.