In the Snap! Forums and also the Scratch website, when you scroll down the header stays at the top of the screen. However, when you scroll down in the Snap! website, it doesn't.
Indeed, it should be consistent. But it wasn't clear to me reading your post which you prefer!
We'll get to the sticky header thing at some point.
probably the one in the title
Isn’t is as simple as display: sticky; or is there something I don’t undertsand?
It's a matter of having development time to work on the site, mostly. And making sure the site still works on all devices and screen sizes.
Okay, forgive me if I'm wrong here, but as a hobbyist HTML designer myself, and I don't see how this would be a problem. Unless this would cover up too much of the screen on mobile devices? I was able to write a JS script that adds this feature pretty quickly, and I'm pretty sure that implementing it into the website would be even easier. Here's the script, by the way:
document.getElementsByClassName('pure-menu-horizontal')[0].style = 'position: fixed; z-index: 1000; background-color: #2d3142'
document.getElementById('wrapper').style = 'margin-top: 48px';
Edit: If anyone wants to try this out, paste it into the browser console on one of the main site pages. If you absolutely cannot wait for this to be implemented then you can use one of those JS script managers that automatically runs a script when you load the page, I guess. (Also I fixed something in the script in this edit. If you're getting layering issues, try using this version instead)
None of the HTML is hard, but there's literally been very little development put into the front-end in the past few months because no one is paid to work on it.
Also if you really want, you can try to edit the Snap!Site codebase: https://github.com/snap-cloud/snapsite 
It's just "things that aren't broken" or preventing someone from using Snap! aren't getting attention right now.
Alright, cool. Does this count as "discussing the change I wish to make with the owners of this repository"?
Yes. Just, as Michael said, try out your mod on your phone.
What do I need to do for the webserver to work? When I compile, all of my pages are stuck at a loading screen, and I'm pretty sure that's why. If I try to compile with a webserver, then it gives me an error that says "no http server in [file path]".
Oh. Right. You have to build a Discourse server on some virtual system somewhere in order to debug this. I bet someone like @spaceelephant or @snapenilk or @ego-lay_atman-bay can walk you through that.
they're talking about the cloud site -- not discourse. Unfortunately the front end assumes there's a web server, you could try editing the JS to connect to snap.berkeley.edu. Or you could look at snap-cloud/snapCloud on github and run a local server yourself.
Thanks, that sounds like the best option.
Update: I edited the first two lines in statics/js/base.js. Now it's looking for a file called "cloud.js" in static/libs. I'm assuming that it's something that appears when I compile Snap with a webserver, and that it has something to do with the snapCloud project, but what should I replace the file path with?
I have never used discourse. As far as I can tell, it works.
I know I'm pretty technical, but that's not something I could do (I would just search google how to do it)
ditto