Now that we can better customise <select> elements, it’s only natural to side-eye other form <input> types that have caused us visual headaches.

Sure, we should be applying the lightest of touches to form elements, especially, but even with a bit of visual-massaging, checkboxes are limited, aside from a bit of accent-color.

There is a brighter future incoming, if you’re to read the spec:

The ::checkmark pseudo-element represents an indicator of whether the item is checked, and is present on checkboxes, radios, and option elements.

— W3C forms level 1

Match that with appearance: base, which is also incoming, and we’re looking at this sort of CSS:

input[type="checkbox"] {
  appearance: base;
}

input[type="checkbox"]::checkmark {
  content: url("data:image/svg+xml,%3Csvg aria-hidden='true' focusable='false' width='24' height='24' viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'%3E %3Cpath fill='none' stroke='currentColor' stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='m5 12l5 5L20 7' /%3E %3C/svg%3E");
}

We’re miles off from that capability yet — it doesn’t look like any browser is working on it — so allow me to show you how to build a nice custom checkbox pattern for until we have the browser capabilities we’re after.

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HTML first, always

It’s always right to start with some good quality markup:

<label for="custom-checkbox" class="checkbox">
  <span class="checkbox__box">
    <input type="checkbox" name="custom-checkbox" id="custom-checkbox" value="Some value that this control toggles">
    <svg aria-hidden="true" focusable="false" width="24" height="24" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg">
      <path fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="m5 12l5 5L20 7" />
    </svg>
  </span>
  <span>A long label for this checkbox to make sure we get a nice wrapping behaviour</span>
</label>

The markup is pretty straightforward here. Inside the parent <label> — which is linked to the input both by being a parent and the for/id attributes — we have a container for the input and icon, along with a text label.

The reason I’m using <span> elements here is because aside from the input/SVG only phrasing content is permitted. I don’t think a <div> would do any harm here, but it’s best to do things right.

On the SVG checkmark element, there’s an aria-hidden="true" attribute. This stops the SVG — a visual element — getting in the way for assistive technology. I’ve also added focusable="false". This is actually a relic from the Internet Explorer days hell, but I keep it on visual only icons, just in case.

Right, we’re in good shape. Let’s make it look good.

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Some CSS

The first thing to do is layout:

.checkbox {
  display: flex;
  align-items: baseline;
  gap: 1em;
  text-wrap: balance;
}

Flex is more than capable here. I like to align on the baseline in this sort of context because as the viewport gets small and the text wraps, we don’t want a vertically centered layout. It looks rubbish!

Speaking of balance, I’m using text-wrap: balance here for the same compressed viewport context and dealing with wrapping text. Keeping a consistent edge (rag) is extra important for small microcopy, such as labels.

Let’s tackle the input itself.

.checkbox input {
  margin: 0;
  width: 100%;
  height: 100%;
  appearance: none;
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 0.2em; /* This is so the focus ring has a matching radius to the visual box */
}

We’ve got to be really careful here because we don’t want to mess up the focusability of our element. Combining appearance: none and absolute positioning, our element is still there, but its no longer in the way, visually. It can still receive focus and will present a focus ring, which is exactly what we need!

Let’s tackle the “box” part, which is also this <input>’s parent.

.checkbox__box {
  position: relative;
  background: transparent;
  color: currentcolor;
  border: 1px solid;
  width: 1.4em;
  height: 1.4em;
  transform: translateY(0.75ex);
  flex-shrink: 0;
  border-radius: 0.2em;
}

A lot of this is self explanatory but I’ll pick up the key parts:

1. I’m using position: relative so the <input> stays inside this box
2. The transform rule is a bit of a magic-number but because it’s a relative ex unit, it scales quite nicely, regardless of parent font size. Most importantly the ex enhances that baseline alignment and fixes the initial alignment of the <input>

Let’s deal with the SVG checkmark next:

.checkbox__box svg {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  pointer-events: none;
  display: none;
  width: 1em;
  height: 1em;
}

The idea here is to visually hide the checkmark when the checkbox isn’t checked and show it when it is. We’ll deal with that CSS next.

.checkbox__box:has(input:checked) {
  background: white;
}

.checkbox__box input:checked + svg {
  display: block;
}

We’re in checked state territory here. I’m setting a white background using :has() which is yet another useful use-case for this endlessly handy addition to CSS.

The following block of CSS uses a traditional next sibling selector to show the SVG element when the input is checked. You could use :has() here too, if you’re feeling fancy.

With all of that CSS in place, we’re looking good.

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This approach could also work for radio buttons

There’s nothing stopping you using this approach for radio buttons. Check out this demo where I’m using a circle icon instead of a checkmark. It works well!

The em units usage allows this whole component to scale

The eagle eyed amongst us will have noticed that aside from the transform rules, I’ve consistently use em units. The reason for this is so our checkbox can scale with no other intervention.

The only change here, versus the first demo is a font-size declaration on the .checkbox component.

A handy pattern, right?

A big thanks to Jake Archibald and Heydon Pickering for checking my homework.