Trimming Transitions or Audio Cross Fades

The duration of transitions or audio cross fades can be changed by trimming in the same way with clips.
While dragging the transition start or end, two clips over which the transition is set are played back simultaneously. You can adjust the duration of the transition with viewing the scene change.

To trim the transition without changing the total length of the timeline clips

In the Settings menu of the Monitor window, check "Expand clip that does not change time" in the Timeline tab.
When the In side of the transition/audio cross fade is dragged, for example, the In clip expands but the Out clip shrinks, and the total length of the both clips are unchanged.