Vertical Menu - Footer Menu

Hm, without Basis (directly or as a base theme), everything should work out of the box.  If you use Basis, the issue is the following definition from core/themes/basis/css/component/footer.css:

.l-footer .menu > li {

  float: left;

}

In that case, theming is necessary, I guess:

 .l-footer .menu > li {

  float: none;

}

Place menu blocks or content blocks into the footer and apply to the parent container

.l-footer-inner {
   display: flex;
   justify-content: center;
}
and
.l-footer-inner > div {
   width: 25%; 
}

https://www.w3schools.com/css/css3_flexbox.asp