Alter UI elements to indicate once they have focus and only when they have focus

[mirror176]

Once something is clicked on it often takes over some input like keypresses and may take an extra click to get focus off of it. This seems best explained by just pointing out examples of it being indicated different from what is really being done.

Clicking on a category in the 'submit segment' popup when there is multiple segments will place focus there. It is easy to tell where focus is while the combobox is brought up listing choices but once selecting one the box closes. At this time that box still has focus; pressing 'f' to toggle fullscreen of the video doesn't work as that hotkey is captured to change the category to 'filler tangent/jokes'. Clicking to the left of the category but still within the sponsorblock popup will move focus away from the category and shared keys like 'f', 'm', 'space bar', etc. go back to the video player. There is no visual indication that the box has focus.

What items display focus is inconsistent: category and action do not while start and end time boxes do. Tabbing to category or action does mark them visually but does not mark the category help button visually and focus does go to it between them.

Further confusion comes from buttons on youtube's toolbar where clicking to start a segment on a video does not mark it with focus, then pressing space will start/stop the video 'and' mark the stop segment button as having focus. Tabbing through objects to put focus on the mark segment button will show it as focused and and pressing space toggle that button and not start/stop the video.

Not having hotkeys shared between youtube's interface and sponsorblock's interface would help avoid some errors when focus is wrong and would have an advantage of being able to control the player and sponsorblock without needing to switch focus but being able to follow where focus is at is more important to avoid the errors.

[mirror176]

Not sure if it is different in other browsers, but these were observed under Firefox.