styles.css

body {
  margin: 0px;
  background: #0f0f0f;
  color: #fff;
  font-family: 'Courier New', Courier, monospace;
  font-size: 22pt;
  font-weight: bold;
}

.background {
  position: absolute;
  display: block;
  top: 0;
  left: 0;
  z-index: 0;
}

h2 {
  text-align: center;
  margin: 0;
  margin-bottom: 8px !important;
}

a {
  color: #15ff00;
}

.container {
  background: #3f00a6;
  padding: 30px;
  display: inline-block;
  border: 2px solid #fff;
  box-shadow: 0px 9px 10px -1px #000;
  z-index: 2;
}

.centered {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
}

#input {
  font-family: 'Courier New', Courier, monospace;
  font-size: 0.8em;
  padding: 12px;
  border: 2px solid #fff;
  background: #070012;
  outline: none;
  width: 700px;
  color: #f2f2f2;
  text-align: center;
}

p {
  text-align: center;
  margin: 0;
}

.form {
  display: flex;
  flex-direction: column;
  align-items: center;
}

#answer, #warning {
  margin-top: 50px;
  background: #320085;
  padding: 20px;
  border-left: 2px solid #fff;
  font-size: 0.8em;
  box-shadow: 0px 2px 7px -1px #000;
}

#warning {
  border-left: 2px solid red;
  background: #a53400;
}

.green {
  color: #0dff5e;
}

.red {
  color: #ff2445;
}

.visible {
  display: block !important;
}