Width of a flex item doesn't change when I use %

Issue

As far as I know, width of a flex item adjusts to its content(when flex-direction: row;).

Here you see, the width of second .item is too long even though I set the width of h1 to 50%.

      * {
        margin: 0;
        padding: 0;
      }
      .container {
        display: flex;
        justify-content: space-between;
        border: 2px solid red;
        padding: 10px;
      }
      .item {
        border: 1px solid black;
      }
      .test {
        width: 50%;
      }

    <div class="container">
      <div class="item">Lorem ipsum dolor sit amet.</div>
      <div class="item">
        <h1 class="test">
          Lorem ipsum dolor sit amet, consectetur adipisicing elit. Commodi,
          quo.
        </h1>
      </div>
    </div>

But when I use px instead of %, the result that I wanted comes out. (Please view it in a full page)

      * {
        margin: 0;
        padding: 0;
      }
      .container {
        display: flex;
        justify-content: space-between;
        border: 2px solid red;
        padding: 10px;
      }
      .item {
        border: 1px solid black;
      }
      .test {
        width: 400px;
      }

    <div class="container">
      <div class="item">Lorem ipsum dolor sit amet.</div>
      <div class="item">
        <h1 class="test">
          Lorem ipsum dolor sit amet, consectetur adipisicing elit. Commodi,
          quo.
        </h1>
      </div>
    </div>

I can't understand how % is calculated in the first code. Can somebody help? Thanks

Solution

You have to apply the width on the .item element.

* {
  margin: 0;
  padding: 0;
}

.container {
  display: flex;
  justify-content: space-between;
  border: 2px solid red;
  padding: 10px;
}

.item {
  border: 1px solid black;
}

.item:nth-child(2) {
  width: 50%;
}

<div class="container">
  <div class="item">Lorem ipsum dolor sit amet.</div>
  <div class="item">
    <h1 class="test">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit. Commodi, quo.
    </h1>
  </div>
</div>

Answered By - Akshay