<p id="em">padding: 2em</p>
<p id="px">padding: 32px</p>

p {
  font-size: 16px;
}

#em {
  padding: 2em;
}

#px {
  padding: 32px;
}

p {
  background-color: thistle;
  width: 300px;
  text-align: center;
}

html {
  font-family: arial;
}