Features: flex-wrap and object-fit:cover, keeps aspect ratio.
I added: gutter, radius, border, hover border, dropshadow, linkable, ul:after spacer,
real-world layout with sidebar.
Possible downsides: Zoom-crop. Portrait images are small/half. FOUC of border and
drop-shadow while lazy-loading! With modern font sizes you'll likely need 20-30vh rather
than 40. Also may need to make these media queries play nicely with your own chosen ones.
Have to override boostrap UL margin or padding, and common/Normalize LI list-style.
