Web designers will use custom buttons, custom link colors, poorly designed webfonts, have 20 scroll jacking animations on a page, giant fucking text, the worst color choices imaginable, 200MB stock photos unrelated to the content of the site but will absolutely flip their shit if you even suggest using custom scrollbars because modifying the normal scrollbars is bad UX because users are retarded and will get confused if your scrollbar looks like the ones from Windows 7. Also if your site looks even slightly different from whatever ridiculous flat design trend they're on right now they will crucify you for bullying disabled people.