Ok, I took a quick look and that’s where I would start.
Add this code at the end of testing the css file so that it can be modified easily, but once you modify it, you can integrate it correctly because it contains new rules and derogations.
#colophon {
grid-template-columns:1fr 1fr 1fr;
}
#colophon > *{
display:flex;
justify-self:center;
border-left:none;
}
.wp-block-page-list,
.wp-block-categories-list,
.wp-block-social-links {
width: auto;
}
.wp-block-image img.wp-image-62 {
width: 100%;
max-width: none;
}
.home .entry-content figure,
.home .entry-content div:nth-child(2),
.home .entry-content div:nth-child(3) {
flex: 1 0 0;
}
.home .entry-content figure {
max-width: 500px;
min-width: 200px;
}
@media screen and (max-width: 880px) {
.home .entry-content {
display: block;
}
.home .entry-content figure {
max-width: none;
min-width: 0;
float: right;
width: 180px;
margin: 20px;
}
#colophon {
display: flex;
flex-direction: column;
}
#colophon > * {
border-left: none;
}
}
Your footer was too wide causing a massive scroll bar. So I changed the grid settings, then on smaller screens I centered the menus. You seemed to be trying to match the footer borders to the columns above, but that would be futile unless you had them both contained in a grid. You can’t really match things up by wiring dimensions because it’s a magic number trick that breaks easily. Therefore, I centered the footer and removed the borders and it looks much cleaner in my mind.
For your three columns I adjusted the column widths to better match the large screen, then on the small screen I floated the image to the right and let the text wrap .
You should of course continue to tweak and perhaps reduce the text size a bit for the small screen and your drop caps etc, but I’ll leave that up to you as it’s mostly tweaking.
I’ve only set up one media query to show the process, but you might need another one at smaller widths just to tweak better, but don’t overdo it because you should be able to get away with just a few media queries.
As an exercise I left the header section alone as it also needs to be rearranged, but hopefully you can figure this out on your own now that you have a start. 
With my code in place, you should see a display like the following live screenshots.
Hope this helps but yell if you don’t understand anything.