h1 {
  text-align: center;
}

fieldset {
  width: 20em;
  background-color: lightgray;
  box-shadow: 5px 5px 5px gray;
  margin-left: auto;
  margin-right: auto;
}

label {
  float: left;
  width: 7em;
  clear: left;
  text-align: right;
  padding-right: 1em;
}

input {
  float: left;
}

button {
  display: block;
  margin-top: 8em;
  margin-left: auto;
  margin-right: auto;
  clear: both;
}

input:required {
  border: 1px solid blue;
}

input:invalid {
  color: white;
  background-color: red;
}