styles.css

main {
  text-align: center;
}

input[type=text], input[type=password], input[type=submit], #key {
   appearance: none;
   border: 1px solid #555;
   padding: 1.5em;
   margin: 1em;
   font-size: 15px;
   line-height: 1.2em;
   width: 80%;
   background: #fff;
   box-shadow: 1px 1px 1px #fff;
   border-radius: 0.5em;
   border: 1px solid #bbb;
}

input[type=submit] {
  width: 83.5%;
}

.modal {
	position: fixed;
	font-family: Arial, Helvetica, sans-serif;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background: rgba(0,0,0,0.8);
  z-index: 99999;
  opacity: 0;
  transition: opacity 400ms ease-in;
  pointer-events: none;
}

.modal > div {
  width: 80%;
  position: relative;
  margin: 10% auto;
  padding: 5px 20px 13px 20px;
  border-radius: 10px;
  background: #fff;
}

@media (min-width: 40em){
  .modal > div {
    width: 32em;
  }
}

.close {
  background: #606061;
  color: #ffffff;
  line-height: 25px;
  position: absolute;
  right: -12px;
  text-align: center;
  top: -10px;
  width: 24px;
  text-decoration: none;
  font-weight: bold;
  border-radius: 12px;
  box-shadow: 1px 1px 3px #000;
  cursor: pointer;
}

.close:hover {
  background: #00d9ff;
}

.pointer {
  cursor: pointer;
}

.hidden {
  display: none;
}

.block {
  display: block;
}