Unable to get ::after of class of selected

.sample-class{
     color: red;
}

.sample-class::after{
   content:'';
   color: black;
}

I can't get the css rule of a class with '::after'

cssComposer.getClassRule("sample-class", {state: 'after'})

is there a way to get

content:'';
color: black;

since the only state I know were 'hover', and 'active'

Thank you !