form-field-example.html

<style>
  .fieldset {
    min-width: 0;
    margin: 0 0 1rem;
    padding: 0;
    border: 0 solid transparent;
  }
  .legend {
    box-sizing: border-box;
    display: table;
    width: 100%;
    max-width: 100%;
    margin: 0 0 .5rem;
    padding: 0;
    font-weight: 600;
    line-height: inherit;
    white-space: normal;
    color: inherit;
  }
</style>

<fieldset class="fieldset">
  <legend class="legend">Fieldset legend</legend>
  <label>
    <input type="checkbox">
    Checkbox
  </label>
</fieldset>