body {
  margin: 0;
  font-family: 'Creepster', cursive;
  background-color: #0a0a0a;
  color: #f5f5f5;
  overflow: hidden;
}

.mansion {
  text-align: center;
  padding: 50px;
  animation: flicker 2s infinite;
}

h1 {
  font-size: 3em;
  margin-bottom: 20px;
  text-shadow: 0 0 10px red;
}

.door {
  width: 200px;
  height: 300px;
  margin: 0 auto;
  background: linear-gradient(to bottom, #333, #000);
  border: 5px solid #444;
  position: relative;
  cursor: pointer;
}

.knock {
  position: absolute;
  bottom: 10px;
  width: 100%;
  text-align: center;
  font-style: italic;
  color: #bbb;
}

.cat {
  width: 100px;
  height: 100px;
  background: url('https://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Black_Cat_Icon.svg/1024px-Black_Cat_Icon.svg.png') no-repeat center/contain;
  position: absolute;
  bottom: 20px;
  right: 20px;
  opacity: 0;
  transition: opacity 0.5s ease-in-out;
}

@keyframes flicker {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.8; }
}