In CKEditor if you select style and then the marker style it doesn't correctly work. The span is added but there isn't anything visibly changed. It looks like it uses a style from contents.css rather than an inline style
It's possible some of these other styles are useful in this file too but this one for sure isn't used at all and was reported as an issue.
Click on screenshot for the image where the marker example is. Using this should highlight yellow.