CSS Class/ID dialog box
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ID
Specifies the ID of the current element. You can type an ID in the box, or click the arrow to select from a list of IDs for which styles have been defined in the document or in external style sheets.
Available classes
Provides a list of classes for which styles have been defined in the document or in external style sheets. You can apply a class from this list to the current element by clicking 
.
Applied classes
Lists the classes that have already been applied to the current element, if any. You can remove an applied class by selecting it and clicking 
.