wl-slider inside wl-expansion: thumblabel not visible

[Corvince]

Not sure if this is a problem with wl-expansion or wl-slider, but the combination of the two looks like this:

(thumblabel hidden behind expansion bar)

https://codepen.io/anon/pen/XwQPBG?&editable=true

PS I just found your library and I think it is beyond awesome!