Some enhancements

[cdesiles]

First of all: thank you, this is a lovely project!
I tweaked it to my needs, and made some changes of my own:

<select class="select">...</select>

Can now be simply:

<select>...</select>

The z-index is decremented each time a SelectFx is instantiated (because there were overlapping), and the appendChild(this.selEl) call has been fixed (was inserting as the end of the parent, not at the right place).

I can fork the project and make a merge request, are you interested in?
Cheers,

Jk.