There are two ways to create a new selector:
using menu Edit->New selector..., or using
button in the tool bar.
In the "New selector" dialog you can type selector to be added, or you can select one of generic CSS1 pseudo-elements/pseudo-classes or HTML elements.
Note!, classes should begin with point (e.g. ".bigtext", "H1.bigtext"); IDs should begin with # (e.g. "#z98", "H1#z98")