What you are going to do next will totally freak you out.
Remove any innocent, cuddly small furry animals from the room . .
Sit comfortably in your chair. . . and .. . just GRAB one of the Timeline Events and PUSH it over the previous one ...
I can hear the screaming in London!
You have just created your very first
CROSSFADE! that's it . .DONE!
Now, you can REALLY get cooking . . where you have your CROSSFADE, you can now drag all mixtures of transitions and so on.
If I think
I THINK what you have been doing, is to treat each Event as an immovable . .er . .stuck Event. No, you can and are invited to push one into the other. I think that is where you are labouring with the lowering of the opacity. If this IS the case then STOP it!!! Immediately!