WebUI: Add delay when closing submenu in WebUI

[vafada]

fixes #23252

this is a CSS-only fix to add a delay when closing the sub-menu in WebUI.

video show it works (ubuntu screen recorder doesn't show the mouse pointer), you can see the copy submenu doesn't go away immediately when the export .torrent menu item gets hovered

Screencast.from.2025-09-09.15-08-45.webm

Though adding a delay can result a small window of overlapping submenu (can be also screen in the video)

[Piccirello]

Haven't tested yet but this is awesome.

[thalieht]

From #23252:

I think, every user chooses the shortest path when moving a mouse cursor. And the shortest path to 'Magnet link' item is diagonal.

IMO this is not fulfilled for all submenus because of

Though adding a delay can result a small window of overlapping submenu (can be also screen in the video)

Try changing a category the way the user above expects and you'll end up with the tags submenu replacing the categories submenu. The window of overlap is not small at all for the purpose described above and the video doesn't really show how annoying it is because there is no interaction with such a submenu when that happens (in the video).

[vafada]

From #23252:

I think, every user chooses the shortest path when moving a mouse cursor. And the shortest path to 'Magnet link' item is diagonal.

IMO this is not fulfilled for all submenus because of

Though adding a delay can result a small window of overlapping submenu (can be also screen in the video)

Try changing a category the way the user above expects and you'll end up with the tags submenu replacing the categories submenu. The window of overlap is not small at all for the purpose described above and the video doesn't really show how annoying it is because there is no interaction with such a submenu when that happens (in the video).

I see. It's because the Tag and Category menu item are on top of each other, moving the mouse diagonally causes the Tag menu to get "hovered"