Flex-grow

Shows how to use flex-grow to make one child element twice as wide as the other.

HTML

<div id="flexbox">
  <div id="big">BIG</div>
  <div id="small">SMALL</div>
</div>

CSS

#flexbox {
  display: flex;
  
  width: 100%;
  height: 300px;
  border: 1px solid black;
}

#big {
  flex-grow: 2;
  
  background-color: lavender;
}
#small {
  flex-grow: 1;
  
  background-color: lightblue;
}