CSS Style form elements ( :indeterminate pseudo-class )

The indeterminate pseudo-class lets you set styles for elements that are in an indeterminate state.

[dailydeveloper]

:indeterminate is a pseudo-class selector in CSS named for a state that is neither checked nor unchecked. It’s that in-between state that we might consider the “Maybe” between “Yes” and “No” options. The state is not fully determined, hence the name: indeterminate.