Fix vertical alignment of icons

[BenjaminSchaaf]

Before:

After:

[kaste]

This seems wrong as there is no vertical-align: center;

On my machine after looks like

[michaelblyons]

Does it look okay if you change center to middle?

https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/vertical-align

[BenjaminSchaaf]

Ah, vertical-align: center is a firefox-ism, and doesn't do the same as middle. Seems the modern approach is to use flexbox.

[BenjaminSchaaf]

I've pushed a fix for this.