Ben Myers covers some clear examples of where CSS totally changes what some screen readers announce. For example, some screenreader will see
text-transform: uppercase; on a button label that says "Add" and read it like an abbreviation, "A.D.D."
… Read article “CSS Can Influence Screenreaders”
These cases of CSS messing with our screenreader announcements are initially shocking, perplexing, and maybe even appalling. After all, they seem to conflict with our mental model of CSS, one that's likely been instilled in us since we started learning web development: