This selector is useful to provide a different focus indicator based on the user's input modality (mouse vs. keyboard).

In this example, the :focus-visible selector uses the UA's behavior to determine when to match. Compare what happens when you click on the different controls with a mouse, versus when you tab through them using a keyboard. Note the difference in behavior from elements styled with :focus.

<input value="Default styles" /><br />
<button>Default styles</button><br />
<input class="focus-only" value=":focus only" /><br />
<button class="focus-only">:focus only</button><br />
<input class="focus-visible-only" value=":focus-visible only" /><br />
<button class="focus-visible-only">:focus-visible only</button>

input,
button {
  margin: 10px;
}

.focus-only:focus {
  outline: 2px solid black;
}

.focus-visible-only:focus-visible {
  outline: 4px dashed darkorange;
}

If your code has to work in old browser versions that do not support :focus-visible, check supports of :focus-visible with @supports and repeat the same focus styling in it, but inside a :focus rule. Note that even if you do not specify anything at all for :focus, old browsers will simply display the native outline, which can be enough.

<button class="button with-fallback" type="button">Button with fallback</button>
<button class="button without-fallback" type="button">
  Button without fallback
</button>

.button {
  margin: 10px;
  border: 2px solid darkgray;
  border-radius: 4px;
}

.button:focus-visible {
  /* Draw the focus when :focus-visible is supported */
  outline: 3px solid deepskyblue;
  outline-offset: 3px;
}

@supports not selector(:focus-visible) {
  .button.with-fallback:focus {
    /* Fallback for browsers without :focus-visible support */
    outline: 3px solid deepskyblue;
    outline-offset: 3px;
  }
}

Make sure the visual focus indicator can be seen by people with low vision. This will also benefit anyone use a screen in a brightly lit space (like outside in the sun). WCAG 2.1 SC 1.4.11 Non-Text Contrast requires that the visual focus indicator be at least 3 to 1.

• Accessible Visual Focus Indicators: Give Your Site Some Focus! Tips for Designing Useful and Usable Focus Indicators

It may not be obvious as to why the focus indicator is appearing and disappearing if a person is using mixed forms of input. For users with cognitive concerns, or who are less technologically literate, this lack of consistent behavior for interactive elements may be confusing.

• :focus
• :focus-within
• A polyfill for :focus-visible