What happens when the flex item width depends on the width of flex-container which is not specified?

General
1 
<!DOCTYPE html>
<html>
    <head>
        <title>Hello, World!</title>
        <link rel="stylesheet" href="styles.css" />
    </head>
    <body>
          <div class="parent">
            <div class="child">
              <div class="item">1</div>
              <div class="item">2</div>
              <div class="item">3</div>
              <div class="item">4</div>
              <div class="item">5</div>
              <div class="item">6</div>
              <div class="item">7</div>
              <div class="item">1</div>
              <div class="item">2</div>
              <div class="item">3</div>
              <div class="item">4</div>
              <div class="item">5</div>
              <div class="item">6</div>
              <div class="item">7</div>
              <div class="item">1</div>
              <div class="item">2</div>
              <div class="item">3</div>
              <div class="item">4</div>
            </div>
          </div>
    </body>
</html>

style.css

.parent {
    display: flex;
    width:50%;
    background-color: blue;
}

.child {
    display: flex;
    flex-wrap: wrap;
    align-items: flex-start;
    aspect-ratio: 1;
    background-color: green;
}
.item {
    width: calc(100% / 7);
    aspect-ratio: 1;
    padding: 1%;
    background-color: red;
    box-sizing: border-box;
}

The child div width is not covering the whole width of parent.
According to me since there is no constraints of width the default behaviour of flex-item is to be the size of the content inside of it.
But since the content inside of it width is dependent on the parent itself, its causing a problem.
image output
Code Link: 42ruxwq27 - HTML - OneCompiler

I tried adding width as 100%, which resulted in the output that i desired, but most importantly

What i want is to know about this behaviour more when the child is dependent of the parents width and the parent is dependent on the childs width.

2

Breakdown of the Code:

  • .parent: This div is the flex container, and its width is set to 50% of the viewport.
  • .child: This div is the flex item container, and it has flex-wrap: wrap , meaning its items will wrap to the next line if they don’t fit within the container’s width.
  • .item: These are the individual flex items. Their width is calculated as 1/7th of the parent container’s width using calc(100% / 7) .

Behavior Explanation:

  1. Flex Item Width Calculation: The width of each .item is calculated based on the width of the .child container. Since the .child container’s width is not explicitly specified, it takes on the available space within the .parent container.
  2. Content-Based Sizing: As you correctly noted, flex items tend to be as wide as their content unless explicitly constrained. In this case, the content within each .item is a simple text node, which doesn’t have a fixed width.
  3. Flex Container Growth: Since the .child container’s width depends on its items, and the items’ widths depend on the container’s width, there’s a circular dependency. This can lead to the container growing slightly larger than necessary to accommodate its items.

Addressing the Issue:

To ensure that the .child container occupies the full width of the .parent container and that the .item s are evenly distributed, you can use the following approaches:

1. Specify a Fixed Width for the .child Container:
CSS

.child {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-start;
  aspect-ratio: 1;
  width: 100%; /* Set a fixed width for the child container */
  background-color: green;
}

This will force the .child container to take up the entire width of its parent, ensuring that the .item s are distributed evenly.

2. Use flex-grow on the .items:

CSS

.item {
  flex-grow: 1; /* Allow items to grow to fill available space */
  aspect-ratio: 1;
  padding: 1%;
  background-color: red;
  box-sizing: border-box;
}

This will make the .item s expand to fill the available space within the .child container, ensuring that they occupy the entire width.