I had to add the following lines to the source html page where i put the spreadshirt-javascript in:
<style id="spreadshop-font">body{font-family: Raleway,sans-serif;background-color:#F6F6F6;}</style>
<link rel="stylesheet" type="text/css" href="https://fonts.googleapis.com/css?family=Raleway:500,600,700,400)" />
otherwise the font did not load.
website: www.hodler.fashion or https://shop.spreadshirt.nl/hodler/
Is this a known issue?
It’s not an issue, it’s by design (feature).
As I remember correctly, SPRD decided to remove default font to keep it simple to overwrite it.
Well, it was an issue for me. How should I know this without debugging it myself?
Well I understand your concerns, but the intention was that the shop takes the font which is used in the overall website. If you haven’t got a font defined in the website where the shop is embedded into, then there is no font the shop can use.
Here are some topics I found, even one of mine, because I ran into the same issue:
Ok, thanks for your replys! 
Is there some documentation somewhere about these kind of things? Like a developer site or something like that?
Actually we started working on exactly that - a guide to the Javascript integration and common pitfalls. It will be published soon, so stay tuned! In the meantime, you can of course continue to ask your questions here in the forum, we will try to help.
Thats great, thanks for your reply.
I thought I had already seen like a Confluence site or something with all kinds of things like this (and with users posting questions/comments), but I cant find it anymore. Do you have a link maybe? I don’t think it was https://developer.spreadshirt.net
As far as I know, that documentation is offline for now, as it is outdated and actively being worked on.