<aside>
  <p>🚨 Sorry, your browser doesn't support <code>:has()</code> - view this demo in <a href="https://caniuse.com/css-has" target="_blank">a supported browser</a>.</p>
</aside>

<div class="selection-groups">
  <fieldset>
    <legend>Select a few colors</legend>
    <div class="selection-options">
      <label><input type="checkbox" name="red"> Red</label>
      <label><input type="checkbox" name="orange" checked> Orange</label>
      <label><input type="checkbox" name="yellow" checked> Yellow</label>
      <label><input type="checkbox" name="green" checked> Green</label>
      <label><input type="checkbox" name="blue"> Blue</label>
      <label><input type="checkbox" name="indigo"> Indigo</label>
      <label><input type="checkbox" name="violet" checked> Violet</label>
      <label><input type="checkbox" name="black"> Black</label>
      <label><input type="checkbox" name="white"> White</label>
    </div>
  </fieldset>
</div>

.selection-options {
  /* Range of checked items */
  /* Yes, this could just be label:has(:checked) but we're demonstrating
  selecting a range :) */
  label:has(:checked):has(~ label :checked),
  label:has(:checked):not(label:has(+ label :checked)) {
    border-inline-color: black;
    background-color: palegreen;
  }

  /* First checked item in a range
  OR top of a single checked item */
  label:has(:checked):not(label:has(:checked) + label) {
    --radius-tl: 0.75em;
    --radius-tr: 0.75em;

    border-block-start-color: black;
  }

  /* Last checked item in a range
  OR bottom of a single checked item */
  label:has(:checked):not(label:has(+ label :checked)) {
    --radius-bl: 0.75em;
    --radius-br: 0.75em;

    border-block-end-color: black;
    box-shadow: 0 4px 3px -2px hsl(0 0% 0% / 35%);
  }
}

.selection-groups {
  border-radius: 1rem;
  background-color: white;
  padding: 2rem;
  font-size: 1.15rem;
  accent-color: mediumvioletred;
}

.selection-groups legend {
  font-weight: 500;
  font-size: 1.1rem;
}

.selection-groups fieldset {
  border: none;
  padding: 0;
}

.selection-options {
  display: grid;
  margin-block-start: 1rem;
}

.selection-options label {
  display: flex;
  align-items: center;
  gap: 0.5em;
  padding: 0.5em;
  border: 1px solid transparent;
  border-radius: var(--radius-tl, 0) var(--radius-tr, 0) var(--radius-br, 0)
    var(--radius-bl, 0);
}

/* :has() support alert */
aside {
  max-width: 30ch;
  padding: 1rem;
  background-color: palegoldenrod;
  border-radius: 0.5rem;
  margin-block-end: 1rem;
  line-height: 1.3;

  code {
    font-size: 1.25em;
    color: firebrick;
  }
}

@supports selector(:has(+ *)) {
  aside {
    display: none;
  }
}