.topnav
{             
text-align: center;  
background-color: #333;
overflow: hidden;
}

.topnav a {        
display: inline-block;
color: #f2f2f2;
text-align: center;
padding: 14px 16px;
text-decoration: none;
font-size: 17px;
}

.topnav a:hover {
background-color: #4CAF50;
transition: 0.250s;
color:white;

}
/* 
.topnav a:active {
    background-color: #ddd;
    color: black;
    } */