Nav. Button font size to bold problem

Please help, here’s the site I’ve been looking everywhere to change the navigation buttons weight to bold,

https://stagging-3.bermanz.co.za/about-us-alt/

nav .menu li {
position: relative;
display: inline-block;
float: left;
font-size: 18px;
margin: 8px 0;

nav .menu ul.sub-menu li {
width: 100%;
position: relative;
display: block;
background: none repeat scroll 0 0 transparent;
border-bottom: 1px solid transparent;
float: none;
margin: 0;
padding: 0;
font-weight: bold;
font-size: 13px;
height: auto;
z-index: 42;
-webkit-backface-visibility: hidden;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;

Nothing happens when I change it to bold.