I thought I did that before I asked. I somehow got it to work since then, or at least it is pretty close (haven’t tested other desktops yet though). Container is now set to full width/contained. Header is set to content width and margin is 20 px; margin on footer is also 20 px. If I could set the container or page margins then I would know they all will stay the same.
I also put in custom css site-header{width:90%;}
site-content{width:90%;}
site-footer{width:90%;}
container {width: 100%;}
but I don’t think it made a difference.