.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
  width: 90%;
}
.flex-container > div {
  display: flex;
justify-content: center;
align-items: center;
height: 20vh;
  }
  
  body {
          font-family: Arial, Helvetica, sans-serif;
        }
        
        .mobile-container {
          max-width: 790px;
          margin: auto;
          background-color: #764d2d;
          height: 1220px;
          color: white;
          border-radius: 20px;
        }
        
        .topnav {
          overflow: hidden;
          background-color: #333;
          position: relative;
        }
        
        .topnav #myLinks {
          display: none;
        }
        
        .topnav a {
          color: white;
          padding: 14px 16px;
          text-decoration: none;
          font-size: 17px;
          display: block;
        }
        
        .topnav a.icon {
          background: black;
          display: block;
          position: absolute;
          right: 0;
          top: 0;
        }
        
        .topnav a:hover {
          background-color: #ddd;
          color: black;
        }
        
        .active {
          background-color: black;
          color: white;
        }
        
        .centerr {
          display: block;
          margin-left: auto;
          margin-right: auto;
          width: 100px;
        }