It's the type of hotel where you're expected to dress for dinner. 去那家酒店赴宴要着正装。
She went to her room to rest for a while before dressing for dinner.
The concept of dressing for dinner was new to her and she found it faintly ridiculous.
In those days, of course, people dressed for dinner.
Are we expected to dress for dinner, do you know?
See also: dress verb (PUT ON CLOTHES)