<p id="msg"></p>
<iframe src="https://develop.kimizuka.org/post-message/?develop"></iframe>

@import url('https://fonts.googleapis.com/css2?family=Exo+2:wght@900&display=swap');

iframe {
  display: none;
}

p {
  display: flex;
  align-items: center;
  justify-content: center;
  position: fixed;
  top: 0; bottom: 0;
  left: 0; right: 0;
  color: #FAFAFA;
  font: 88px 'Exo 2', sans-serif;
  background: #212121;
}

window.addEventListener('message', function(evt) {
  try {
    const json = JSON.parse(evt.data);
    
    console.log(json);
    
    document.getElementById('msg').innerText = json.txt; 
  } catch (err) {
    console.log(err);
  }
});