Focus is not visible after migration to 3.x.x

After migration to 3.x.x we cannot see anymore where the current focus is on. So I'm tabbing in my form and in 2.5.x.x you could see a dotted border around the current button. Seems like this one is hidden in IE and FF. In Chrome this works. I would like to know how I can influence this. I don't have any experience with this is CSS. Anyone who could help me?
1 answers

Use the CSS selector :focus. See also w3schools.