date-range-combo-box.html

<!-- instance -->
<date-range-combo-box>
  <input type="date" content-slot="start">
  <input type="date" content-slot="end">
</date-range-combo-box>

<template element="date-combo-box">
  <content slot="date"></content>
</template>

<template element="date-range-combo-box">
  <date-combo-box>
    <content slot="start" as="date"></content>
  </date-combo-box>
  <date-combo-box>
    <content slot="end" as="date"></content>
  </date-combo-box>
</template>