.c-footer__wrapper {
  border-top: 1px solid var(--c-text-body);
  display: flex;
  align-items: flex-start;
  justify-content: flex-start;
  flex-wrap: wrap;
  padding-top: 1rem;
}

.c-footer__column:first-child {
  flex-grow: 1;
  margin-right: 1rem;
}

.c-footer__wrapper {
  border-top: 1px solid var(--c-text-body);
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  flex-wrap: wrap;
  padding-top: 1rem;
}

Reduce width of theme picker in site footer
Reduce width of theme picker in site footer

Having the `<details>` element fly all the way across the screen was
pretty awkward. Instead, use `justify-content: space-between` on the
footer wrapper so it's only as large as necessary.

I may revisit once I have more theme controls in there. For now, this
looks/feels better.
