Flexbox
CSS layout model for one-dimensional arrangements — rows or columns. display: flex on the container. Solved the center-vertically problem once and for all.
W3C Candidate Recommendation 2012, broad browser support 2015. justify-content (main axis), align-items (cross axis), flex-wrap, flex-grow/shrink/basis. Distinct from CSS Grid (two-dimensional). Modern advice: use Flexbox for component structures (toolbar, cards), Grid for page layouts. Quiz is everyone's favorite: Flexbox Froggy + Grid Garden (learning games).