<card-form>>

  <input slot="number">

  <input slot="month">

  <input slot="year">

</card-form>

<script>

  const shost = document.querySelector('card-form');

  shost.attachShadow({mode: 'open'});

  shost.shadowRoot.innerHTML = `

    <label>Number<slot name="number"></slot></label>

    <label>Month</label><slot name="month"></slot><label>Year</label><slot name="year"></slot>

`;  

</script>