You should be able to remove it using
outline: none;
but keep in mind this is potentially bad for usability: It will be hard to tell whether an element is focused, which can suck when you walk through all a form's elements using the Tab key - you should reflect somehow when an element is focused.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…