One of the best ways to find works of criticism on theatre topics is running a subject search. Subjects are assigned to items in strings that follow certain rules. For this topic, your string should start with:
Drama
or
Theater
If you search for "Drama" as a subject, it will return all related items. You can narrow these results by adding a time period:
Drama -- 19th century
Drama -- 20th century
You can narrow this further and specifically target works of criticism:
Drama -- 19th century -- History and Criticism
If you're still getting too many results or have something very specific in mind, you can narrow even further:
Drama -- 19th century -- History and Criticism -- Bibliography
Drama -- 19th century -- History and Criticism -- Congresses
Drama -- 19th century -- History and Criticism -- Periodicals
Drama -- 19th century -- History and Criticism -- Indexes
If you search for "Theater" you can add the phrase "History and Criticism" without a region or time period:
Theater -- History and Criticism
You can run a search under the "Subject" tab in the catalog and browse the results to find other strings that might be helpful to you specifically.
If you find that you're having difficulty using the catalog or finding the kind of information you're looking for, please don't hesitate to ask for help!