The DB uses a font called Fira Sans, which you can see on Google Fonts here. I don't think this is a font that is installed by default on PCs, so you'll have install it yourself if you want to use it on Word and such. Though, many basic sans-serif typefaces can replicate the look -- I can hardly tell this font apart from ones like Calibri and Arial.
The site's source code also says that it will try to use Tahoma, Ubuntu, Trebuchet MS, Helvetica, Arial and any sans-serif font -- in that order -- if it cannot use Fira Sans. So if the site's font looks off for you, it's probably because the site couldn't load the external font and found the first one it could use from that list. Reloading the page usually fixes this, since it may have just failed to load it once.
Protip, if you're ever curious what font is being used or more widely, how a website is formatted, Chrome has a feature that lets you find this out immediately by looking at source code. It finds the relevant info for you instantly. Just right click whatever part you want to see and click "Inspect". HTML and CSS are pretty straightforward to read even if you're not really familiar with them.
