The code defines two CSS pseudo-classes, `:focus` and `:focus-visible`. `:focus` is...

The code defines two CSS pseudo-classes, :focus and :focus-visible.

:focus is applied to an element when it becomes the active element within its parent container. In this case, the CSS rule sets the background color of the focused element to pink.

:focus-visible is similar to :focus, but it only applies when the element is focused using a keyboard or other non-mouse input method. This can be useful for accessibility purposes, as it helps users who rely on keyboard navigation to understand where their focus is on the page. The CSS rule in this case sets a red outline with a thickness of 3 pixels around the element when it gains focus through non-mouse input methods.