How to change button style on focus change?

Question

css

Good afternoon. I need to change the style of a button when I press (hold) and move the focus to another element. Suppose there are 2 buttons, I click on one and delay and move the focus to another element by pressing tab, the style of the first button should change.
Tried to do it by button:active:not(:focus). But the style only changes when the focus of the window itself changes, using alt+tab. I will be grateful if I get an answer.