Indeterminate state checkboxes are not supported

[Greg-Smulko]

Indeterminate state checkboxes are not supported.
The "indeterminate" state looks the same as "not checked" now (empty box), but should look differently.

I think this line causes the problem:

honeycomb-web-toolkit/src/forms/css/raw/_honeycomb.forms.raw.forms.scss

Line 22 in fa90793

appearance: none;