look at the title
It shouldn't be there...

It kind of looks ugly with barely any margin/ padding

bugs.html says:

"To avoid this, do not have multiple tabs of Crystal Cobves open"

instead
of

"To avoid this, do not have multiple tabs of Crystal Coves open"

the favicon cycle has seemed to stop working.
:(

why document.querySelector when you have jQuery?

don't keep old files, github has you covered!
seriously, you can go back to your older commits and just take stuff from there, instead of just keeping your old file as extra data

it has none, like the known bugs,

get an icon that everybody will remember, instead of just all the ores.
Get like a beautiful icon that is very memorable. 🌈

You could use it just for Credits and Known bugs, but I recommend it to be as all of the favicons. :P

where art poley?
poley poley poley
poley square

Instead of moving it to only the top of the mine, could you move it to a specific position?
I'm asking this, since when I got a diamond, I forgot it was rare and went on, when I should've been happy... (since I was mining low)

(tis, a dum idea)

The left banner can't close, so much of the screen isn't shown, could you add a js button that hides it and opens it when wanted?

Don't ask them to make a github account, just make them email you. or me.

Also add that at the bottom of your pages
use <footer>

This is much easier for them, for it is likely that they have an email.

Asking for a github account might make them a bit suspicious, and also, if they're just going to add to one project, but don't want to code anything else, don't make them make a github account

why does the left banner have a horizontal scroll bar?
(p. s. don't have horizontal scroll bars unless absolutely necessary)

Could there be a music slider, where it changes the music volume?
I want to hear the mining sound effect much, but music is too loud. :(

'keypress' is apparently deprecated, so use keydown or something

the popup says "rare spawn", but since this is a mining game... shouldn't it be "rare find" or something like that?

the link color is hard to read, change it to a light color or people might not see a link is there