For example:
https://jigsaw.w3.org/css-validator/validator?uri=https%3A%2F%2Fdocs.opencv.org%2F5.x%2Fd4%2Fd17%2Fnamespacecv_1_1aruco.html&profile=css3svg&usermedium=all&warning=1&vextwarning=&lang=en

I already addressed two which are from upstream in doxygen/doxygen#11546 & doxygen/doxygen#11545, but the css of this project introduces a few more.