I discovered different behavior of the CheckBox control:
If you click the checkbox there is no border around the checkbox which emphasises the focus.
However, if you skip to the control with the tab key, it gets a thicker rounded corner, which has the color of the themeColor.
Is this by design?
What I want, is that it gets this thicker border also when I click it with the mouse.
You can see this behavior in the Adobe Flex Explorer.
That is by design. When focused by keyboard, the component is highlighted
by a focus rectangle. It is not part of the component's skin. You can
modify the skin to show a thicker border if you want.
How can I do it?
The only skinnable properties are afaik upSkin, overSkin, downSkin, disabledSkin.
Nothing applies to the focus.