Added custom CSS to header but have lost the fixed position on blog page

Hi there, 

I'm not sure if I'm even articulating this properly so bear with me! I've added custom CSS to my header to split the navigation on my header which worked great. However, on the blog page the posts are lost under the header now, and I can't work out how to fix the header or to bring the blog posts down.

Can someone help with the code?

Here's what I added for the split navigation. 

.header-nav {
 position: absolute;
 margin-top:0!important;
 top: 0rem; 
}

.header-nav-item:nth-of-type(2) {
 margin-right: 50vw!important; 
}

.header-title {
 z-index: 99!important;
 } 
}
 

Thanks! 

Hi @mrs_kate_dyson, can you share the url of the page on which you are seeing the issue?