Flags not centered in mobile menu

First of all, great plugin! Highly appreciate your work.

My problem:

I only use the flags in my main menu and they work very well in the desktop version. However in the mobile version, the flags wouldn’t be vertically centered. I haven’t found a workaround yet.

Here’s a screenshot of the situation:
http://imgur.com/qcew9cq

Appreciate your help!

https://ww.wp.xz.cn/plugins/polylang/