How to make fade handle icon show on top right of audio track?

How do you make the little icon show up in the top right of an audio track where you can drag it to create a fade? (See attached image)
fade.jpg

Adjust fade handle brightness…?

thank you for the idea, but the icon is completely gone so the brightness doesn’t affect it, anyone else know why the icon may be missing from all my audio tracks and how to get it to appear?