You aren't clear about a fade, as in crossFADE and overlap, or a plain FADE at the front and end of an Event?

Anyways the ways I know are:

1] Thru': Options > Preferences > Editing > Automatically Overlap . . . This ONLY happens when you add media - then events - to timeline. You can't do this in post-addition. To do post addition you'd need a script.

. .soooo....

2] A freebie Script, somewhere? . . . .

3] Excalibur - Edward Troxel

4] Ultimate S Pro - VASST

Using 1] has little variation, but with 3] & 4] there is far greater depth of control PLUS you get a massive stack of invaluable extra tools too!

Up to you?

Grazie