Style compare map

[olafveerman]

There are some default Mapbox styles that mess up the compare map on the bottom of a disaster page:

Removing overflow: hidden; from .mapboxgl-map results in this:

[ascalamogna]

@olafveerman I think there's something wrong with the slider, when I try to remove the overflow: hidden on all elements I get this. I'm not sure it's a styling issue. Can we get a dev to look at this?