Fold horizontal navbar menu into drop-down menu on narrow screens

[bluebirch]

Make sure you go through the Hexo docs, Icarus user manual, and GitHub issues to see if the feature you are requesting has been already addressed by others.

Is your feature request related to a problem? Please describe.

On narrow screens (mobile), the navbar top menu becomes a horizontally scrollable section if it doesn't fit.

Describe the solution you'd like

I'd like the horizontal menu to fold into a drop-down menu.

Describe alternatives you've considered

My alternative so far is to have as few items in the menu as possible. Three or four works, for most of the time, five or more doesn't. And I want five or six items.