<a href='...' download>...</a>

you can style a link to look like a button if you care about the difference.

but traditionally, references to files are links, and it is up to the browser what to do with them (whether to just download them or to download and then display them). that's what all links are. that's the whole point of hypertext. every link causes the browser to make a request to a server and fetch something. buttons are for activating things, not for downloading.