У вашего броузера проблема в совместимости с HTML5
Hey gang, in this CSS Flexbox tutorial, I'll show you how we can use the flex-grow property to allow our flex elements to grow into all of the space available to them. Flex grow is essentially the rate at which elements can grow in relation to their sibling flex elements.
----- COURSE LINKS:
+ Source files on GitHub - https://github.com/iamshaunjp/css-flexbox-playlist
+ Brackets editor - https://brackets.io/
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