How to remove border on click on element in slick slider?

Question

css

I'm making a slider using the slick slider plugin and I can't understand where this blue border around the block comes from when the element is clicked:

It is not in the style files, the blocks everywhere have outline: none in slick.css and slick.theme.css.
Bootstrap styles don't seem to have anything similar for divs either .

Answer 1

outline: none add for slick-slide:active

Answer 2

.slick-slide:active, .slick-slide:focus {
outline: none;
}

Answer 3

Helped as a result of applying the outline: none property to the slider elements.