::Before/::After + Flexbox in Mdn

::before/::after + flexbox in MDN

This was implemented in bug 867454. Not implementing it was a mistake, as comment #0 tells.

The spec says:

The contents of a flex container consists of zero or more flex items: each in-flow child of a flex container becomes a flex item, and each contiguous run of text that is directly contained inside a flex container is wrapped in an anonymous flex item.

And that does include ::before/::after pseudo elements (at least the mozilla folks interpret it this way now, and I'd concur).

"Firefox 23 for developers" also features this information, explicitly referring to ::before and ::after as "in-flow".

In-flow ::after and ::before pseudo-elements are now flex items (bug 867454).

Is there any polyfill for current CSS Flexible Box Layout Module as per W3C CR (display: flex etc.)?

There's currently no polyfill that implements the W3C Candidate Recommendation.

The author of flexie.js mentioned some time ago that he was working on updating flexie.js but there has not been anything published since then. So it's hard to say if or when it will actually materialize.

CSS style for ::after with plus(+) selector

This isn't going to be possible in pure CSS.

In the accepted version of this answer I was entirely wrong about the reason for this! I've always assumed that the ::after pseudo-element was placed after the element -- hence, y'know, the name -- but apparently I've been wrong about that for years; the ::before and ::after pseudo-elements are actually first and last children of the main element. Many thanks to @MRNafisiA for pointing this out in comments!

Except not really, because they're still not treated as part of the DOM. Sibling selectors can not be used to match pseudo-elements, and they will not be included in any other selectors that would normally match child elements (first-child, last-child, etc).

So the closest you can get is probably input:checked::after {} (though some extra layout fiddling is necessary to get past the sort-of-zero-width checkbox.)

label {display: block}

input::after {
  content: "A";
  color: red;
  margin-left: 1.2em;
}

input:checked::after {
  color: blue
}

<label><input type="checkbox"></label>
<label><input type="checkbox"></label>
<label><input type="checkbox"></label>

Why is ::before pseudo element taking up room in flexbox?

The first thing to know is that pseudo elements applied to a flex container become flex items (MDN).

Therefore, your container (.test) has three flex items, with the ::before being just another sibling.

Is there a way to tell flex to ignore ::before & ::after?

Yes. Remove the pseudo element from the document flow. Use absolute positioning.

I would expect the width here to be 100% (200px).

Once the ::before is removed from the document flow, it will be free to expand across the container.

.test {  height: 200px;  width: 200px;  display: flex;  flex-direction: row-reverse;  position: relative;  /* new */}
.test::before {  position: absolute; /* new */  background-color: yellow;  content: "";  height: 100%;  width: 100%;  opacity: 0.04;}
.first {  background-color: green;}
.second {  background-color: grey;  flex: 1;}
body {  background-color: purple;}

<div class="test">  <div class="first">       </div>  <div class="second">       </div></div>

Better way to set distance between flexbox items

• Flexbox doesn't have collapsing margins.
• Flexbox doesn't have anything akin to border-spacing for tables (edit: CSS property gap fulfills this role in newer browsers, Can I use)

Therefore achieving what you are asking for is a bit more difficult.

In my experience, the "cleanest" way that doesn't use :first-child/:last-child and works without any modification on flex-wrap:wrap is to set padding:5px on the container and margin:5px on the children. That will produce a 10px gap between each child and between each child and their parent.

Demo

.upper {
  margin: 30px;
  display: flex;
  flex-direction: row;
  width: 300px;
  height: 80px;
  border: 1px red solid;

  padding: 5px; /* this */
}

.upper > div {
  flex: 1 1 auto;
  border: 1px red solid;
  text-align: center;

  margin: 5px;  /* and that, will result in a 10px gap */
}

.upper.mc /* multicol test */ {
  flex-direction: column;
  flex-wrap: wrap;
  width: 200px;
  height: 200px;
}

<div class="upper">
  <div>aaa<br/>aaa</div>
  <div>aaa</div>
  <div>aaa<br/>aaa</div>
  <div>aaa<br/>aaa<br/>aaa</div>
  <div>aaa</div>
  <div>aaa</div>
</div>

<div class="upper mc">
  <div>aaa<br/>aaa</div>
  <div>aaa</div>
  <div>aaa<br/>aaa</div>
  <div>aaa<br/>aaa<br/>aaa</div>
  <div>aaa</div>
  <div>aaa</div>
</div>

How to set a fixed width column with CSS flexbox

You should use the flex or flex-basis property rather than width. Read more on MDN.

.flexbox .red {
  flex: 0 0 25em;
}

The flex CSS property is a shorthand property specifying the ability of a flex item to alter its dimensions to fill available space. It contains:

flex-grow: 0;     /* do not grow   - initial value: 0 */
flex-shrink: 0;   /* do not shrink - initial value: 1 */
flex-basis: 25em; /* width/height  - initial value: auto */

---

A simple demo shows how to set the first column to 50px fixed width.

.flexbox {  display: flex;}.red {  background: red;  flex: 0 0 50px;}.green {  background: green;  flex: 1;}.blue {  background: blue;  flex: 1;}

<div class="flexbox">  <div class="red">1</div>  <div class="green">2</div>  <div class="blue">3</div></div>

In CSS Flexbox, why are there no justify-items and justify-self properties?

Methods for Aligning Flex Items along the Main Axis

As stated in the question:

To align flex items along the main axis there is one property: justify-content

To align flex items along the cross axis there are three properties: align-content, align-items and align-self.

The question then asks:

Why are there no justify-items and justify-self properties?

One answer may be: Because they're not necessary.

The flexbox specification provides two methods for aligning flex items along the main axis:

1. The justify-content keyword property, and
2. auto margins

---

justify-content

The justify-content property aligns flex items along the main axis of the flex container.

It is applied to the flex container but only affects flex items.

There are five alignment options:

• flex-start ~ Flex items are packed toward the start of the line.

  

• flex-end ~ Flex items are packed toward the end of the line.

  

• center ~ Flex items are packed toward the center of the line.

  

• space-between ~ Flex items are evenly spaced, with the first item aligned to one edge of the container and the last item aligned to the opposite edge. The edges used by the first and last items depends on flex-direction and writing mode (ltr or rtl).

  

• space-around ~ Same as space-between except with half-size spaces on both ends.

  

---

Auto Margins

With auto margins, flex items can be centered, spaced away or packed into sub-groups.

Unlike justify-content, which is applied to the flex container, auto margins go on flex items.

They work by consuming all free space in the specified direction.

---

Align group of flex items to the right, but first item to the left

Scenario from the question:

• making a group of flex items align-right (justify-content: flex-end)
  but have the first item align left (justify-self: flex-start)

  Consider a header section with a group of nav items and a logo. With
  justify-self the logo could be aligned left while the nav items stay
  far right, and the whole thing adjusts smoothly ("flexes") to
  different screen sizes.

---

Other useful scenarios:

---

Place a flex item in the corner

Scenario from the question:

• placing a flex item in a corner .box { align-self: flex-end; justify-self: flex-end; }

---

Center a flex item vertically and horizontally

margin: auto is an alternative to justify-content: center and align-items: center.

Instead of this code on the flex container:

.container {
    justify-content: center;
    align-items: center;
}

You can use this on the flex item:

.box56 {
    margin: auto;
}

This alternative is useful when centering a flex item that overflows the container.

---

Center a flex item, and center a second flex item between the first and the edge

A flex container aligns flex items by distributing free space.

Hence, in order to create equal balance, so that a middle item can be centered in the container with a single item alongside, a counterbalance must be introduced.

In the examples below, invisible third flex items (boxes 61 & 68) are introduced to balance out the "real" items (box 63 & 66).

Of course, this method is nothing great in terms of semantics.

Alternatively, you can use a pseudo-element instead of an actual DOM element. Or you can use absolute positioning. All three methods are covered here: Center and bottom-align flex items

NOTE: The examples above will only work – in terms of true centering – when the outermost items are equal height/width. When flex items are different lengths, see next example.

---

Center a flex item when adjacent items vary in size

Scenario from the question:

• in a row of three flex items, affix the middle item to the center of the container (justify-content: center) and align the adjacent
  items to the container edges (justify-self: flex-start and
  justify-self: flex-end).

  Note that values space-around and space-between on justify-content property will not keep the middle item centered in relation to the container if the adjacent items have different widths (see demo).

As noted, unless all flex items are of equal width or height (depending on flex-direction), the middle item cannot be truly centered. This problem makes a strong case for a justify-self property (designed to handle the task, of course).

#container {  display: flex;  justify-content: space-between;  background-color: lightyellow;}.box {  height: 50px;  width: 75px;  background-color: springgreen;}.box1 {  width: 100px;}.box3 {  width: 200px;}#center {  text-align: center;  margin-bottom: 5px;}#center > span {  background-color: aqua;  padding: 2px;}

<div id="center">  <span>TRUE CENTER</span></div>
<div id="container">  <div class="box box1"></div>  <div class="box box2"></div>  <div class="box box3"></div></div>
<p>The middle box will be truly centered only if adjacent boxes are equal width.</p>

---

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