css - First-child full-width in Flexbox - Stack Overflow

How can I set the first-child of flexbox in full-width and all of the other childs set to flex:1(for split space)? Like this

css - First-child full-width in Flexbox - Stack Overflow

css - First-child full-width in Flexbox - Stack Overflow

css - First-child full-width in Flexbox - Stack Overflow