style.css

* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
      }
body {
      background: yellow;
      width: 100%;
      height: 100%;
}
form {  
      text-align: center; 
      align-content: center;
      background: white;
      width: 80%;
      margin: 10%;
      border-radius: 5px;
      padding: 10%;
      }

input[type=number], select {
            width: 80%;
            padding: 12px 20px;
            margin: 8px 0;
            display: inline-block;
            border: 1px solid #ccc;
            border-radius: 4px;
            box-sizing: border-box;
            font-size: 30px;
            text-align: center;
          }

.result {
      margin-top: 20px;
      font-size: 20px; 
      color: white;
      background-color: rgb(4, 49, 69);
      border-radius: 10px;
      padding: 8px;

      }

span {
          
      }

.btn{
  
        
  }
button {
      border: none;
      background: green;
      color: rgb(255, 255, 255);
      padding: 10px 22px;
      text-align: center;
      text-decoration: none;
      display: inline-block;
      font-size: 16px;
      margin: 4px 2px;
      cursor: pointer;
      border-radius: 5px;
            
      }
#reset{
      background: rgb(245, 26, 6);
      color: rgb(255, 255, 255);
            
      }