I'm having an issue in 2019 where if I select a face to mate parts in an assembly the entire part has a light blue line around it, instead of Just the face I'm selecting turning dark blue.  I must have hit something by accident & I have NO idea what I've done!  I can still mate parts together, but it's making it more confusing as I add more parts to my assembly.  Has anyone ever experienced this?  I tried searching, but couldn't find anything like my problem. 

Thanks!