body{font-family:Arial,sans-serif;padding:20px}body,html{margin:0;padding:0}*{box-sizing:border-box}form{display:flex;flex-direction:column;width:400px;margin:0 auto}input,textarea,button{margin-bottom:20px;padding:10px;font-size:18px}input[type=checkbox]{margin:0}button{background-color:#4caf50;border:none;color:#fff;text-align:center;display:inline-block;transition-duration:.4s;cursor:pointer}button:hover{background-color:#45a049}button.valid{background-color:#4caf50}button.invalid,button.hover{background-color:#d3d3d3}