About the transition tag seems to be invalid for the class attribute

Question

.two{width: 100px;height: 100px;background: #FF6500;transition: width 2s;}.two:hover{width:450;}p{width: 200px;height: 200px;background: #ff6500; transition: width 2s;}p:hover{width: 500px;}

The above code is valid for p tag, but invalid for .two, how to solve it