Allow switching and selecting themes with the keyboard

In desktop, allow moving across the elements of a popover with direction keys. Also allow to select one of the elements with the space bar or enter key.

Use case: when designing a screenshot, I switch between themes to see which one fits better. Instead of scrolling and clicking themes, I would like to navigate and select themes using the keyboard. I think it’s better from the UX perspective. These improvement can be applied to any element of any popover.