Widget has its own background

[theiskaa]

The Hidable has its own background, with elevation and background color, probably it takes the material common color of theme, so, in my case white.

In any case we should remove the Material widget from under the Hidable.
Otherwise there is no way to avoid this issue:

The white parts (on top-left and top-right) is Hidable's background, which actually should be transparent.