<details>
  <summary>Your favourite cars list</summary>
  <form>
    <fieldset>
      <legend>Cars</legend>
      <ul>
        <li>
          <label for="bmw">BMW<input type="checkbox" id="bmw" name="bmw" value="bmw"></label>
        </li>
        <li>
          <label for="citroen">Citroen
          <input type="checkbox" id="citroen" name="citroen" value="citroen"></label>
        </li>
        <li>
          <label for="skoda">Skoda
          <input type="checkbox" id="skoda" name="skoda" value="skoda"></label>
        </li>
        <li>
          <label for="volvo">Volvo
          <input type="checkbox" id="volvo" name="volvo" value="volvo"></label>
        </li>
      </ul>
    </fieldset>
  </form>

</details>
details {
  border: 1px solid #767676;
  border-radius: 3px;
  display: inline-flex;
  flex-direction: column;
  padding: 3px 6px;
}

details summary::marker {
  display: none;
  font-size: 0;
}

details summary::-webkit-details-marker {
  display: none;
  font-size: 0;
}

details summary::after {
  content: "\25BC" / "";
  display: inline-block;
  font-size: 0.6rem;
  height: 1rem;
  line-height: 1rem;
  margin-left: 0.5rem;
  position: relative;
  transition: transform 0.25s;
}

details[open] summary {
  margin-bottom: 1rem;
}

details[open] summary::after {
  top: -0.15rem;
  transform: rotate(180deg);
}

form {
  display: flex;
}

fieldset {
  border: 0;
  padding: 0;
  width: 100%;
}

fieldset legend {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}

ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

ul li {
  border-radius: 3px;
  margin: 0;
  padding: 4px 2px;
}

ul li:hover {
  background: #eee;
}

ul li label {
  display: flex;
  flex-grow: 1;
  justify-content: space-between;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.