Floats were never intended for layout, however clever developers found ways in which to use them to create their layouts. Having worked with floats you may have noticed some limitations and bugs (clearfix anyone? vertical centering?).
Flexbox is a new layout mode in CSS3 initially developed by Mozilla to make layouts. There were 3 different iterations of the flex property, the final 2012 spec —
display: flex has excellent browser support. The current Flexbox spec is fully supported in all modern browsers, including mobile, IE11 and Edge.
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