Hi Kevin, in that find this CSS in the Customiser > Additional CSS:
/* ------
Fixed Header
------- */
@media (min-width: 769px) {
body {
margin-left: 200px; /* Change to match width below */
}
.site-header {
position: fixed;
left: 0;
top: 0;
width: 200px; /* Change width */
z-index: 300;
height: 100%;
overflow: auto;
overflow-x: hidden;
-webkit-backface-visibility: hidden;
-webkit-overflow-scrolling: touch;
transition: .1s ease;
}
.admin-bar .site-header {
top: 32px;
}
.site-header .main-navigation li {
float: none;
}
}
I have commented here the two properties you need to change. Just set them to px’s you need.