If this is already known to some, sorry, but I've been looking for it for a long time.
It's always been annoyingly hard for me to see when an event is selected, especially when I'm zoomed out on the timeline. I finally found a setting in the Internal Preferences (Event Selection Outline Thickness) which increases the border around selected events from the default of 0 (i.e. NO border; why is that the default?!?!?) to whatever. I chose a border of 6, and now when I select an event(s) there is a big fat blue border around it making it obvious what's selected no matter how I'm zoomed on the timeline.
Yippee!