Using focus-within to style input groups

Input groups, popularlized by Bootstrap, is a pattern that includes an input with a label and/or a button element.

<div class="input-group">
  <div class="input-group-prepend">
    <label for="name">Name</label>
  </div>
  <input type="text" name="name" id="name" />
</div>

We wrap the elements in a div with a class of input-group. We will use this element to provide our focus styles. We also wrap our label in an element with a class of input-group-prepend which allows us to add a border to the right of the label. We could also have a input-group-append class which would add a border to the left of the label.

Now that we have our markup structure in place, we can start to apply our styling to the elements.

.input-group {
  display: inline-flex;
  border: 1px solid #ddd;

  input {
    padding: 1rem;
    border: 0;
    font: inherit;

    // Since we are providing an alternative focus
    // style, it is safe to remove the focus styling
    // from the input itself
    &:focus {
      outline: none;
    }
  }

  label {
    padding: 1rem;
  }
}

Now we can now watch for focus within our input group and adjust our border color and apply a box-shadow.

.input-group {
  &:focus-within {
    border-color: #05f;
    box-shadow: 0 0 0 0.25rem rgba(13, 110, 253, 0.25);
  }
}

View the demo.