@charlag sure, gmail for example will strip a position: fixed so you can't overflow outside the email content section. I can't really tell if cohost strips anything since I don't have an account, but they seem to give users a lot of options so uhh, yeahh
imo there's also a big difference between clicking an email which then influences the screen, versus scrolling through a timeline where anything could show up (and mess with your cursor, for example)