Multiselect: On desktop drop-down options lose background fill

[natalia-fitzgerald]

Describe the bug
When options are shown on desktop and the user scrolls through the options, the background fill is lost after the user scrolls past the first 3 options.

Related issue:
#1164

To Reproduce
Steps to reproduce the behavior:

1. Visit https://www.consumerfinance.gov/about-us/blog/
2. Click on a multiselect.
3. Type something if the options don't show up.
4. Scroll down in the options past the first 3 and see that the background behind the options scroll away.

Expected behavior
Background should say opaque behind the options.

Screenshots

[anselmbradford]

I see this in Safari 16.6 (18615.3.12.11.2)