CODEWITHSUNDEEP
htmlcssflexbox
Andrew Graber
Andrew Graber

Reputation: 187

How to evenly distribute width between flexbox children with nested flexboxes?

I am working on some css3 for a website I'm building. I'm attempting to make a "container" class that uses flexbox to make all its children have equal width. This works properly, but when I put a "container" and a normal element inside another "container", the two children are not of equal width.

I'm not sure why this isn't working, as it works for any element that is not a container.

HTML:

<div class="container">
  <div class="container">
    <div class="content-box">
      One Sixth
    </div>
    <div class="content-box">
      One Sixth
    </div>
    <div class="content-box">
      One Sixth
    </div>
  </div>
  <div class="content-box">
    One half
  </div>
</div>

CSS:

.container {
    display: flex;
    align-items: flex-start;
}

.container > * {
    flex-basis: 100%;
    min-width: 0;
}

.container > :not(:first-child) {
    margin-left: 2%;
}

Codepen example: https://codepen.io/NetworkOverflow/pen/XLbdqa

Upvotes: 3

Views: 11877

Answers (2)

Bryce Howitson
Bryce Howitson

Reputation: 7690

The problem is when you put a container inside of a container it's adding the margin so you see double the space on the right.

I would set your container to justify-content: space-between; which pushes content elements to the outside edges. I'm using flex:1 instead of flex-basis to tell the browser that each element should take up the same amount of space.

Your CSS becomes:

.container {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
}

.container > * {
    flex: 1;
    margin-left: 2%;
    min-width: 0;
}

.container > *:first-child {
    margin-left:0;
}

/* not needed
.container > :not(:first-child) {
    margin-left: 2%;
}
*/

Update:

Depending on the usage, it's sometimes helpful to add "sizing" classes that force a flex-basis based on the number of items. Here's a codepen example.

.third {
  flex-basis: calc(33.3333% - 2%);
}
.half {
  flex-basis: calc(33.3333% - 2%);
}

Upvotes: 5

Michael Benjamin
Michael Benjamin

Reputation: 371231

You're paying a price for setting all elements to flex-basis: 100%.

Because you're telling all elements, regardless of the number of siblings they may have, to occupy the full width of the container, you're forcing flex-shrink to calculate the space necessary to accommodate them all.

This involves a relatively complex flexbox algorithm, which gets even more complex when you factor in padding and box-sizing: border-box, both of which exist in your code.

The algorithm is explained here: How does flex-shrink factor in padding and border-box?

The quickest and easiest solution would be to specify the actual width of the containers.

For the row illustrating the problem (with a container, and a container within a container), instead of setting them to flex-basis: 100%, which triggers flex-shrink, set them to flex-basis: 50%. Now the flex-shrink process is avoided and you get what you want.

I added this to your code:

.container > .demo50 {
  flex-basis: 50%;
}

revised demo

div.content {
  float: left;
  width: 100%;
  height: 100%;
  background-color: var(--background-color2);
  padding: 2% 10%;
}

div.banner {
  background-color: var(--scheme-color2);
  box-shadow: 0px 0px 50px 10px rgba(23, 196, 167, 0.5);
  padding: 1rem;
  text-align: center;
  margin-bottom: 2em;
}

.content-box {
  background-color: var(--background-color1);
  box-shadow: 0px 0px 10px 5px rgba(84, 84, 84, 1);
  padding: 1rem;
  overflow-wrap: break-word;
  margin-bottom: 2em;
}

.container {
  display: flex;
  align-items: flex-start;
}

.container > * {
  flex-basis: 100%;
  min-width: 0;
}

.container > :not(:first-child) {
  margin-left: 2%;
}

.two-thirds {
  flex-basis: calc(100% / 3 * 2);
}

.container > .demo50 {
  flex-basis: 50%;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --background-color1: #707070;
  --background-color2: #424242;
  --background-color3: #afafaf;
  --scheme-color1: #20f9d5;
  --scheme-color2: #17c4a7;
  --scheme-color3: #89e5d6;
  --text-color: #e3edeb;
}

body {
  font-family: "Open Sans", sans-serif;
  color: var(--text-color);
}
<div class="content">
  <div class="container">
    <div class="banner">
      <h1>Example</h1>
    </div>
  </div>
  <div class="container">
    <div class="content-box">
      <p>Using 'flex-basis: 100%' seems to work perfectly well for evenly sizing and spacing elements in a row. However, when you put a .container inside a .container and attempt to do something like you see two rows below, the .container element and the
        element that follows do not space themselves at half and half width.</p>
    </div>
  </div>
  <div class="container">
    <div class="content-box">
      One Half
    </div>
    <div class="content-box">
      One Half
    </div>
  </div>
  <div class="container">
    <div class="container demo50">
      <div class="content-box">
        One Sixth
      </div>
      <div class="content-box">
        One Sixth
      </div>
      <div class="content-box">
        One Sixth
      </div>
    </div>
    <div class="content-box demo50">
      One half
    </div>
  </div>
  <div class="container">
    <div class="content-box">
      One Third
    </div>
    <div class="content-box">
      Two Thirds
    </div>
    <div class="content-box">
      Three Thirds
    </div>
  </div>
  <div class="container">
    <div class="content-box two-thirds">
      Two Thirds
    </div>
    <div class="content-box">
      One Third
    </div>
  </div>
  <div class="container">
    <div class="content-box">
      One Third
    </div>
    <div class="content-box two-thirds">
      Two Thirds
    </div>
  </div>
</div>

Upvotes: 1

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