Alternatively, you could use a font-size with a unit that’s relative to the screen width (vw). So e.g. in your example you could use font-size: 4vw instead of font-size 60px. It’s not a perfect solution, but very simple and quick. You can read more about this here for example:
Looking at my code, my tweet button was actually kind of broken, but I’ve fixed it now. There’s different ways to do twitter buttons, but I wanted something lightweight, so I just made mine a link with the url for creating a tweet. Then when a new quote is generated, I can just change the href of the link to include the text of that quote.