Ok, so on your site, I can see the secondary var is set to this:
While the default colour would have been: #ffffff
Your colour (eef47f) is very close to the colour that is now used for the highlight, since the update, and that’s why you no longer see a difference.
What you can do:
Solution 1
Reset the secondary variable back to its default. This will impact the general look of the site, and turn your light-blue background back to white
Solution 2
Target the specific highlight variable via CSS and change it to something else with higher contrast.
The variable used is:
background-color: var(--d-unread-notification-background);