Expand and roll up icons in ContentBoxWdg() are not visible

[diegocortassa]

Describe the bug
Expand and roll up icons in ContentBoxWdg() are not visible

To Reproduce
Steps to reproduce the behavior:

1. GO to a view using ContentBoxWdg (es. "Users in Groups")
2. See icons in the up-right angle are highlighted when mouse is over but unvisible

Expected behavior
Icons should be visible.

Screenshots

[diegocortassa]

PR #1654 resolve this issue