Force Header, footer and and Images to stay within Squarespace Max Width Margin

Someone please tell me why o why?  Why is it that every time I feel like i've exhausted all remedies and hope on finding an answer and I reach out to this forum, all of a sudden I find it.  It's taken me 2.5 hours to find this answer AND on top of that, it was from on old circle member in this forum (https://forum.squarespace.com/profile/9595-rwp/)

Not sure is he is still on but thank you for this code.  Now I have to figure out then what exactly does the margin-width do but that's another day.  This can be closed.

#header {
    max-width: 1920px;
    margin: auto;
}
section.page-section {
    max-width: 1920px;
    margin: auto;
}