The Experimental Layout Lab of Jen Simmons
labs.jensimmons.com
labs.jensimmons.com
While it's now __possible__ to layout complex designs easily using CSS Grid, it's usually not the best user experience on a phone. Why go to the trouble of making a beautiful layout with lots of white space that won't show on mobile without scrolling?
Yes, you can use media queries to give a better UX on mobile. But if the end result is going to be a single-column page that strips out whitespace for the majority of users, why not just use a collapsing columnar layout?
And not everything has a so vast majority of mobile users that optimizing the experience for desktop/tablet users isn't worth it - especially for sites/SPAs with many elements and very complex layouts.
http://gridbyexample.com/ is another nice resource.
Note that grids — in the Swiss design school sense — are about visual harmony, not just about placing things next to each other horizontally.