First, they changed the background color of the top ads from blue to yellow. No real big deal to advertisers there. It’s the second change that could make a significant difference to your CTR.
Google modified the top ads so that users are required to click on the ad’s link in the top line. You used to be able to click anywhere in the box and you would get taken to the advertiser’s site. Hopefully, this will reduce unintentionally clicked ads and improve the quality of your site visitors.