The phrase on the Styles group title bar interrupts between the subject arrow and the verb opens. There is no punctuation surrounding this interruption because it is essential to help the reader find the exact arrow you are talking about out of all the arrows that might exist on a typical computer screen.
Here there are no commas around Frost’s name because his name is essential to the sentence. It identifies which poet you are talking about. Without his name, the reader would have to ask, “Which poet, out of all the poets in the world and throughout history, are you talking about?”
Notice that if you put his name first, there would be no question of who you were talking about, because his name clearly identifies him. In that case any further description, such as the words a 20th-century American poet, would be a nonessential interruption and require commas:
Here are some additional examples of interruptions:
In sentence 1, the interruption is essential to identifying the book out of all the books in the world. The essential information cannot be surrounded by commas.
In sentence 2 the book has already been fully identified before the interruption. The interruption merely adds additional description that is not needed for identifying the item. Commas are needed.