<solar-system>

by WebComponents

HTML

<solar-system>
  <star-sun>
    <planet-earth>
      <earth-moon></earth-moon>
    </planet-earth>
  </star-sun>
</solar-system>

<style>
  body {
    margin: 0;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: black;
    overflow: hidden;
  }

  /* Undefined custom elements default to display: inline */
  solar-system,
  star-sun,
  planet-earth,
  earth-moon {
    display: block;
  }

  solar-system {
    font-size: 10px;
    width: 40em;
    height: 40em;
    position: relative;
  }

  star-sun {
    position: absolute;
    top: 15em;
    left: 15em;
    width: 10em;
    height: 10em;
    background-color: yellow;
    border-radius: 50%;
    box-shadow: 0 0 3em white;
  }

  planet-earth,
  earth-moon {
    position: absolute;
    border-style: solid;
    border-color: white transparent transparent transparent;
    border-width: 0.1em 0.1em 0 0;
    border-radius: 50%;
  }

  planet-earth {
    top: -10em;
    left: -10em;
    width: 30em;
    height: 30em;
    animation: orbit 36.5s linear infinite;
  }

  earth-moon {
    top: 0;
    right: 0;
    width: 8em;
    height: 8em;
    animation: orbit 2.7s linear infinite;
  }

  planet-earth::before,
  earth-moon::before {
    content: '';
    position: absolute;
    border-radius: 50%;
  }

  planet-earth::before {
    top: 2.8em;
    right: 2.8em;
    width: 3em;
    height: 3em;
    background-color: aqua;
  }

  earth-moon::before {
    top: 0.8em;
    right: 0.2em;
    width: 1.2em;
    height: 1.2em;
    background-color: silver;
  }

  @keyframes orbit {
    to {
      transform: rotate(360deg);
    }
  }
</style>