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CSS ::before and ::after pseudo-elements allow you to insert “content” before and after any non-replaced element (e.g. they work on a <div> but not an <input>). This effectively allows you to show something on a web page that might not be present in the HTML content. You shouldn’t use it for actual content because it’s not very accessible in that you can’t even select and copy text inserted on the page this way —  it’s just decorative content.

In this article, I’ll walk you through seven different examples that showcase how ::before and ::after can be used to create interesting effects.

Note that for most examples, I am only explaining the parts of the code that deal specifically with CSS pseudo-elements. That said, all of the CSS is available in the embedded demos if you want to see the code for additional styling.

Styling Broken images

When a user visits your website, their internet connection (or a factor beyond your control) might prevent your images from downloading and, as a result, the browser shows a broken image icon and and the image’s alt text (if it’s actually there).

How about showing a custom placeholder instead? You can pull this off using ::before and ::after with a bit of CSS positioning.

First, we need to use relative positioning on the image element. We are going to use absolute positioning on one of the pseudo-elements in a bit, so this relative position makes sure make sure the pseudo-element is positioned within the content of the image element, rather than falling completely out of the document flow.

img {
  display: block; /* Avoid the space under the image caused by line height */
  position: relative;
  width: 100%
}

Next, let’s create the region of the broken image effect using the image’s ::before pseudo-element. We’re going to style this with a light gray background and slightly darker border to start.

img::before {
  background-color: hsl(0, 0%, 93.3%);
  border: 1px dashed hsl(0, 0%, 66.7%);
  /* ... */
}

<img> is a replaced element. Why are you using ::before pseudo-element on it? It wont work!. Correct. In this scenario the pseudo-element will show in Chrome and Firefox when the image fails to load, which is exactly what you want. Meanwhile, Safari only shows the styling applied to the alt text.

The styling is applied to the top-left corner of the broken image.

So far, so good. Now we can make it a block-level element (display: block) and give it a height that fills the entire available space.

img::before {
  /* ... */
  display: block;
  height: 100%;
}

We can refine the style a little more. For example, let’s round the corners. We should also give the alt text a little breathing room by giving the pseudo-element full width and absolute positioning for better control placing things where we want.

img::before {
  /* ... */
  border-radius: 4px;
  content: "";
  position: absolute;
  width: 100%;
}

If you stopped here and checked your work, you might be scratching your head because the alt text is suddenly gone.

That’s because we set content to an empty string (which we need to display our generated content and styles) and cover the entire space, including the actual alt text. It’s there, we just can’t see it.

We can see it if we display the alt text in an alternate (get it?) way, this time with help form the ::after pseudo-element. The content property is actually capable of displaying the image’s alt attribute text using the attr() function:

img::after {
  content: attr(alt);

  /* Some light styling */
  font-weight: bold;
  position: absolute;
  height: 100%;
  left: 0px;
  text-align: center;
  top: 1px;
  width: 100%;
}

This is awesome! In Chrome, at least.

But, in Firefox, not so much.

A quick fix is to target the alt attribute directly using an attribute selector (in this case, img[alt]), and target similar styles there so things match up with Chrome.

img[alt] {
  text-align: center;
  font-weight: bold;
  color: hsl(0, 0%, 60%);
}

Now we have a great placeholder that’s consistent in Chrome and Firefox.

Custom blockquote

Blockquotes are quotes or an excerpts from a cited work. They’re also provide a really great opportunity to break up a wall of text with something that’s visually interesting.

There are all kinds of ways to style blockquotes. Chris has a set of five styles that go all the way back to 2007.

I want to look at another technique, one that incorporates ::before and ::after. Like we saw with the last example, we can use the content property to display generated content, and apply other properties to dress it up. Let’s put large quotation marks at the start and end of a blockquote.

The HTML is straightforward:

<blockquote>
  <!-- Your text here -->
</blockquote>

A few cosmetics in the CSS:

blockquote {
  font-style: italic;
  line-height: 1.618;
  font-size: 1.2em;
  width: 30em;
  position: relative;
  padding: 40px 80px;
}

Note the position: relative in there because, as you’ll learn, it’s essential for positioning the blockquotes.

As you’ve probably guessed, we’re going to use ::before for the first quotation mark, and ::after for the closing one. Now, we could simply call the content property on both and generate the marks in there. But, CSS has us covered with open-quote and close-quote values.

blockquote::before {
  content: open-quote;
  /* Place it at the top-left */
  top: 0;
  left: 0;
}

blockquote::after {
  content: close-quote;
  /* Place it at thee bottom-right */
  bottom: 0;
  right: 0;
}

This gets us the quotation marks we want, but allow me to button up the styles a bit:

blockquote::before,
blockquote::after {
  background-color: #cccccc;
  display: block;
  width: 60px;
  height: 60px;
  line-height: 1.618;
  font-size: 3em;
  border-radius: 100%;
  text-align: center;
  position: absolute;
}

Icon Bullet List

We have ordered (<ol>) and unordered (<ul>) lists in HTML. Both have default styling dictated by the browser’s User Agent stylesheet. But with ::before pseudo-element, we can override those “default” styles with something of our own. And guess what? We can use emojis (😊) on the content property!

.name-list li::before {
  content: "😊";
  margin-right: 15px;
  font-size: 20px;
}

While this is great and all, it’s worth noting that we could actually reach for the ::marker pseudo-element, which is designed specifically for styling list markers. Eric Meyer shows us how that works and it’s probably a better way to go in the long run.

Animated toggle switch

One of the neatest tricks for styling forms is creating a toggle switch out of a standard HTML checkbox. In fact, Preethi Sam recently shared one approach for it when showing off a handful of other checkbox styling tricks using CSS masks.

True to its name, a toggle switch is used to toggle or switch between the checked and unchecked states of a checkbox element.

<form class="container">
  <label class="switch">
    <input type="checkbox" />
  </label>
</form>

The customization is all thanks to modifications added to the <input> element via the ::before and ::after pseudo-elements. But first, here is some baseline CSS for the <form> element:

.container {
  background: #212221;
  background: linear-gradient(to right, #1560bd, #e90);
  border-radius: 50px;
  height: 40px;
  position: relative;
  width: 75px;    
}

We’re going to “hide” the checkbox’s default appearance while making it take up the full amount of space. Weird, right? It’s invisible but still technically there. We do that by:

• changing its position to absolute,
• setting the appearance to none, and
• setting its width and height to 100%.

input {
  -webkit-appearance: none; /* Safari */
  cursor: pointer; /* Show it's an interactive element */
  height: 100%;
  position: absolute;
  width: 100%;
}

Now, let’s style the <input> element with its ::before pseudo-element. This styling will change the appearance of the input, bringing us closer to the final result.

input::before {
  background: #fff;
  border-radius: 50px;
  content: "";
  height: 70%;
  position: absolute;
  top: 50%;
  transform: translate(7px, -50%); /* Move styling to the center of the element */
  width: 85%;
}

What, wait? You’d think that ::before wouldn’t work with a replaced element, like <input>. And that’s true, but only when the input type is image which is equivalent to an <img> element. Other form controls, like a checkbox, are defined as non-replaced elements in the HTML spec.

Next, we need to create the “toggle” button and it just so happens we still have the ::after pseudo-element available to make it. But, there are two things worth mentioning:

1. The background is a linear-gradient.
2. The “toggle” button is moved to the center of the <input> with the transform property.

input::after {
  background: linear-gradient(to right, orange, #8e2de2);
  border-radius: 50px;
  content: "";
  height: 25px;
  opacity: 0.6;
  position: absolute;
  top: 50%;
  transform: translate(7px, -50%);
  transition: all .4s;
  width: 25px;
}

Try clicking on the toggle button. Nothing happens. That’s because we’re not actually changing the checked state of the <input>. And even if we were, the result is… unpleasant.

The fix is to apply the :checked attribute to the ::after pseudo-element of the <input>. By specifically targeting the checked state of the checkbox and chaining it to the ::after pseudo-element, we can move the toggle back into place.

input:checked::after {
  opacity: 1;
  transform: translate(170%, -50%);
}

Gradient border

We can decorate images with borders to make them stand out or fit more seamlessly within a design. Did you know we can use a gradient on a border? Well, we can with ::before (there are other ways, too, of course).

The core idea is to create a gradient over the image and use the CSS z-index property with a negative value. The negative value pulls the gradient below the image in the stacking order. This means the image always appears on top as long as the gradient has a negative z-index.

.gradient-border::before {
  /* Renders the styles */
  content: "";
  /* Fills the entire space */
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  /* Creates the gradient */
  background-image: linear-gradient(#1a1a1a, #1560bd);
  /* Stacks the gradient behind the image */
  z-index: -1;
}

figure {
  /* Removes the default margin */
  margin: 0;
  /* Squeezes the image, revealing the gradient behind it */
  padding: 10px;
}

Gradient overlays

This is similar to what we did in the previous example, but here, we’re applying the gradient on top of the image. Why would we do that? It can be a nice way to add a little texture and depth to the image. Or perhaps it can be used to either lighten or darken an image if there’s text on top it that needs extra contrast for legibility.

While this is similar to what we just did, you’ll notice a few glaring differences:

figure::before {
  background-image: linear-gradient(to top right, #1a1a1a, transparent);
  content: "";
  height: 100%;
  position: absolute;
  width: 100%;
}

See that? There’s no z-index because it’s OK for the gradient to stack on top of the image. We’re also introducing transparency in the background gradient, which lets the image bleed through the gradient. You know, like an overlay.

Custom radio buttons

Most, if not all, of us try to customize the default styles of HTML radio buttons, and that’s usually accomplished with ::before and ::after, like we did with the checkbox earlier.

We’re going to set a few base styles first, just to set the stage:

/* Centers everything */
.flex-center {
  align-items: center;
  display: flex;
  justify-content: center;
}

/* Styles the form element */
.form {
  background: #ccc;
  height: 100vh;
  width: 100%;
}

/* Styles the inputs */
.form-row {
  background: #fff;
  border-radius: 50px;
  height: 40px;
  margin: 10px;
  overflow: hidden;
  position: relative;
  width: 150px;
}

Now let’s remove the default styling of the radio buttons, again, with appearance: none;

.form-input {
  -webkit-appearance: none; /* Safari */
  appearance: none;
}

::before should be positioned at the top-left corner of the radio button, and when it’s checked, we change its background color.

.form-input::before {
  /* Renders the styles */
  content: '';
  /* Shows that it's interactive */
  cursor: pointer;
  /* Positions it to the top-left corner of the input */
  position: absolute;
  top: 0;
  left: 0;
  /* Takes up the entire space */
  height: 100%;
  width: 100%;
}

/* When the input is in a checked state... */
.form-input:checked::before {
  /* Change the background color */
  background: #21209c;
}

We still need to iron a few things out using ::after. Specifically, when the radio button is checked, we want to change the color of the circular ring to white because, in its current state, the rings are blue.

.form-input::after {
  /* Renders the styles */
  content: '';
  /* Shows that it's interactive */
  cursor: pointer;
  /* A little border styling */
  border-radius: 50px;
  border: 4px solid #21209c;
  /* Positions the ring */
  position: absolute;
  left: 10%;
  top: 50%;
  transform: translate(0, -50%);
  /* Sets the dimensions */
  height: 15px;
  width: 15px;
}

/* When the input is in a checked state... */
.form-input:checked::after {
  /* Change ::after's border to white */
  border: 4px solid #ffffff;
}

The form label is still unusable here. We need to target the form label directly to add color, and when the form input is checked, we change that color to something that’s visible.

.form-label {
  color: #21209c;
  font-size: 1.1rem;
  margin-left: 10px;
}

Click the buttons, and still nothing happens. Here what’s going on. The position: absolute on ::before and ::after is covering things up when the radio buttons are checked, as anything that occurs in the HTML document hierarchy is covered up unless they are moved to a new location in the HTML document, or their position is altered with CSS. So, every time the radio button is checked, its label gets covered.

You probably already know how to fix this since we solved the same sort of thing earlier in another example? We apply z-index: 1 (or position: absolute) to the form label.

.form-label {
  color: #21209c;
  font-size: 1.1rem;
  margin-left: 10px;
  z-index: 1; /* Makes sure the label is stacked on top */
  /* position: absolute; This is an alternative option */
}

Wrapping up

We covered seven different ways we can use the ::before and ::after pseudo-elements to create interesting effects, customize default styles, make useful placeholders, and add borders to images.

By no means did we cover all of the possibilities that we can unlock when we take advantage of these additional elements that can be selected with CSS. Lynn Fisher, however, has made a hobby out of it, making amazing designs with a single element. And let’s not forget Diana Smith’s CSS art that uses pseudo-elements in several places to get realistic, painting-like effects.

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