html, body {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
  }
  
  .container {
    display: flex;
    height: 100%;
    width: 100%;
    align-items: center;
    justify-content: center;
    animation: 1.5s ease 0s infinite pulse;
  }
  
  .box {
    height: 90%;
    max-height: 400px;
  }
  
  #heart {
    height: 100%;
    margin-left: auto;
    animation: 1.5s ease 0s infinite beat;
  }
  
  @keyframes beat {
    0%, 50%, 100% { transform: scale(1, 1); }
    30%, 80% { transform: scale(0.92, 0.95); }
  }
  
  @keyframes pulse {
    0%, 50%, 100% {  background: #fee; }
    30%, 80% { background: #fff; }
  }