Formatting a menu bar to fit the same length as the logo bar

so im making a nav bar and i would like it to fit under my logo with the same width however the nav bar seems to be shorter in width compared to the logo there making it look funny

here is the css for the logo bar:

.logo{
overflow: hidden;
text-align: left;
position: relative;
margin : 0px 100px ;
height : 60px ;
background-color: white;
color:#1F6C8B;
font-family: Arial;

}

and here is nav bar css

.topnav {
overflow: hidden;
text-align: center;
position: relative;
margin : 0px 100px ;
height : 50px ;
font-family: Arial;

}

.topnav a {
float: left;
color: #f2f2f2;
text-align: center;
padding: 10px 20px;
text-decoration: none;
font-size: 20px;
background-color: #1F6C8B;
height : 25px ;

}