I can't open the tf2 sky list page.

Sorry, I was watching UEAKCrash's beginner mapping tutorials when I hit a brick wall. I cannot open https://developer.valvesoftware.com/wiki/Team_Fortress_2_Sky_List or https://developer.valvesoftware.com for that matter. It just says:

Secure Connection Failed

An error occurred during a connection to developer.valvesoftware.com. PR_CONNECT_RESET_ERROR

I don't know if I can continue without this, but I thought you guys might help out.

Edit:
It seems like developer.valvesoftware.com is a super important tool for mappers, but I still can't connect.

 

works fine for me. If you have a VPN turn it off and try again. If that doesnt work try rebooting your router, as weird as it sounds the internet and its routing protocols can be weird sometimes with traffic.

 

If it's the sky properties you want, this should help. https://tf2maps.net/downloads/all-environment.2401/

 

Well, it's not exactly the same but:
https://wiki.teamfortress.com/wiki/List_of_skyboxes

And you can always explore the decompiled maps from the game to see the maps settings.