What is the use of flex-basis when used with flex-grow and flex-shrink?

HTML-CSS
1

Tell us what’s happening:

I don’t understand the use of flex-basis when we already assigned the flex-grow and flex-shrink values?

Your code so far


<style>
  #box-container {
    display: flex;
    height: 500px;
  }
  #box-1 {
    background-color: dodgerblue;
    flex: 2 2 150px;
    height: 200px;
  }

  #box-2 {
    background-color: orangered;
    flex: 1 1 150px;
    height: 200px;
  }
</style>

<div id="box-container">
  <div id="box-1"></div>
  <div id="box-2"></div>
</div>

Your browser information:

User Agent is: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/responsive-web-design/css-flexbox/use-the-flex-shorthand-property