Just play a move and the draw offer is automatically rejected. Don't know about the difference between PC and mobile though...
How do I decline a draw?

Thanks baddogno.
Yeah, that's what happened. I moved and the game went on. But it seems weird that the browser version of chess.com didn't even tell me that there was a draw offer - or maybe it did and I could not find it. Would be nice if it was front and center, big Y/N buttons.

Ok, more to the point: How do I accept a draw? It happened again today, this time I want to accept the draw but there is nowhere to click "yes". Phone app says draw offered without a way to accept, desktop says nothing.
In a daily tournament game I was offered a draw. On my phone (android app) I can see a draw was offered, but can't see where to decline the draw. When I log onto my PC I can see the same game there, but can't see the draw offer or how to decline it.