Before or after going to the Theatre du Rond-Point des Champs Elysées, you can go to a bar / restaurant called the Berkeley on the avenue Matignon.
When I was there with my wife, we used, like we often do, the service of La Fourchette, because this restaurant was on 50 % discount, which tends to make it very affordable (otherwise, it is a little bit expensive, but what do you expect on the Champs-Elysees ???)
My wife tried the veal with pastas, which was a good choice as she told me the veal was excellent. I had the beef carpaccio and it was a success too, the only disappointment were the french fries, which could have been better and home-made !
Another thing, as very often in the restaurants of the Capitale, the drinks can be very expensive, and that’s the case for water in this restaurant : € 8 for a bottle of water is exaggerated.
But I can say that the place is quite nice, the service is professional too and the food is very honest for this location. You can go there without any hesitation.
If you prefer, on the Matignon avenue, there are lots of trendy lounge bars & restaurants you can try, but beware of the prices, which can be pretty high !