Since background colors were added to the style in the newest versions of Expressive Code, the application of double background to the text leads to the contrast between background and text falling below the requirements.

For example consider the example under Selecting inline marker types (mark, ins, del).

Notice how each of the three markers has a stronger color underneath the text. That's because all <ins>, <del> and <mark> set a low opacity background color. The <span>s inside inherit this background in the absence of one specified and thus the background becomes more prominent.

Can't apologize enough for introducing this bug in my PR.