Applying a style in NG2 (NGTi)

Feedback
1

Having a code line

elements.gridSchoolUnitAssignments.styleClass = 'ag-theme-bootstrap readOnly';

and a corresponding CSS selector

.ag-theme-bootstrap.readOnly {
	color: var(--readOnlyColor);
}

works perfectly in NG1, but not in NG2 (NGTi).

How to accomplish the same result in NG2, i. e. applying a style as shown above?

Regards,