BuddyPress.org

It’s hard for me to guess without seeing the markup. Keep in mind that the css that you’ve posted is looking for a *child* of div.activity-list with the class name “red”. Make sure that the activity item markup still has its CSS class rendered by the following code (in entry.php of your child theme):
`class=””`
or else the filter won’t do anything.

As an aside, I’m not sure what you can do with divs that you can’t do with ul/lis. With a software like BP, in my view it’s better to make changes with CSS if possible, so that your child theme doesn’t override too much of the default theme (thereby making upgrades easier for you).