Why CSS :focus-within is amazing

— 5 minute read

This is not a :focus selector, which will highlight when you focus on an element. But a selector to fire when something within is focused.

In our case, we'll be focusing on forms (I see what you did there 😏)

The end result will look like this:

CSS focus-within selector

HTML Structure

As for our HTML, we wil create a form with 2 inputs.

<form>
  <label for="username">Username</label>
  <input type="text" name="username" />
  <br /><br />
  <label for="password">Password</label>
  <input type="password" name="username" />
</form>

That's all we need for this specific demo.

CSS focus-within pseudo selector

The :focus-within is a pseudo-selector, like :before or :after.

Let's first add some basic styling.

body {
  display: flex;
  min-height: 100vh;
  justify-content: center;
  align-items: center;
}
form {
  border: 1px dashed #333;
  padding: 25px;
}

This will make sure our form is absolutely centered on the page and has a small border to showcase our effect later on.

Now we want to draw the users attention to the form, but making it a fancy colour when they focus an input field.

form {
  border: 1px dashed #333;
  padding: 25px;
  transition: background 0.3s ease;
}
form:focus-within {
  background: #f4d35e;
}

This will change the background of our form to yellow.

You can see this in this Codepen.

See the Pen Why CSS :focus-within is amazing by Chris Bongers (@rebelchris) on CodePen.

Making it more awesome

Yes, we can even make it more awesome by using a box-shadow hack we can create a kind of modal effect!

form {
  border: 1px dashed #333;
  padding: 25px;
  transition: all 0.3s ease;
  box-shadow: 0 0 0 100vmax rgba(0, 0, 0, 0);
}
form:focus-within {
  background: #f4d35e;
  box-shadow: 0 0 0 100vmax rgba(0, 0, 0, 0.7);
}

We create a box-shadow that is 100% of the viewport biggest position (width or height). Initially, this will be at 0 opacity.

When we have a :focus-within we change the opacity to 70%.

The effect is a lightbox-like effect ✨.

See the Pen Why CSS :focus-within is amazing ~ Modal Effect by Chris Bongers (@rebelchris) on CodePen.

Browser Support

The :focus-within selector actually has pretty good support, considering IE is dead already.

CSS focus-within selector browser support

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