Flexbox CSS offers some of the most effective layouts that you can achieve with CSS only, It is supported by all modern browsers and so is a great choice for the layout foundation of any modern website. Here are some of the most useful things you can do with Flexbox CSS:-
Center a Div horizontally & Vertically with Flex CSS
See how to centre a div horizontally and vertically on our Code Pen.
Fluid Equal Height & Width Responsive Columns with Flex CSS
You can add as many flex columns (.flex-col) as you want and they will always be exactly the same width which is equivalent to full-width of .flex-row/number of .flex-col and then will also flex at responsive breakpoints.
See Fluid Equal Height & Width Responsive Columns with Flex CSS on Code Pen.