cjjonesyc's post in Position navigation menu items underneath site title was marked as the answer
Solved this myself. Here's the code if anyones interested:
@media only screen and (min-width:991px) {
.page-section:first-of-type {
padding-top:15px !important;
}
.page-section {
margin-left: 200px;
}
#header {
padding: 40px 10px 10px 0px;
width: 200px;
position: fixed;
height: 100vh;
z-index: 99999 !important;
display: table;
writing-mode: horizontal-lr;
text-orientation: mixed;
}
.header-nav-list {
position: fixed;
flex-direction: column;
text-align: left !important;
left: 4%;
top: 18%;
z-index: 9999;
}
footer.sections .content-wrapper {
margin-left: -200px;
}
}