how to create responsive menu in wordpress

.global_nav ul {
-moz-border-bottom-colors: none;
-moz-border-left-colors: none;
-moz-border-right-colors: none;
-moz-border-top-colors: none;
border-bottom: 1px solid #FFFFFF;
border-image: none;
border-left: 1px solid #FFFFFF;
border-radius: 16px;
border-top: 1px solid #FFFFFF;
height: 30px;
margin-top: 7px;
overflow: hidden;
padding-left: 1px;
padding-top: 5px;
position: absolute;
width: 100px;
}

.global_nav ul li {
display: block;
padding: 0 7px 15px 13px;
}
.global_nav li a {
color: #FFFFFF;
display: inline-block;
float: left;
font-family: Arial,Helvetica,sans-serif;
font-size: 14px;
font-weight: bold;
line-height: 20px;
padding: 3px 26px 5px 3px;
text-transform: uppercase;
}
.global_nav {
margin-left: 0 !important;
}