Give this a try. (Save a copy of your code in case my edit doesn’t work for you so you can put your edit back in)
Remove:
.blog .headerclass,
.category-2 .headerclass,
.category-6 .headerclass,
.page-id-94 .headerclass,
.page-id-276 .headerclass,
.page-id-318 .headerclass,
.postid-1 .headerclass,
.postid-20 .headerclass,
.postid-219 .headerclass,
.postid-228 .headerclass,
.postid-263 .headerclass,
.postid-288 .headerclass,
.postid-310 .headerclass,
.postid-326 .headerclass,
.postid-404 .headerclass {
height: 250px;
background: #fff url(https://www.lifepathbydesign.net/wp-content/uploads/2016/02/BlogBanner.jpg);
width: 100%;
background-repeat: no-repeat;
background-position: center;
}
And replace it with:
@media (min-width: 992px) {
.blog .headerclass,
.category-2 .headerclass,
.category-6 .headerclass,
.page-id-94 .headerclass,
.page-id-276 .headerclass,
.page-id-318 .headerclass,
.postid-1 .headerclass,
.postid-20 .headerclass,
.postid-219 .headerclass,
.postid-228 .headerclass,
.postid-263 .headerclass,
.postid-288 .headerclass,
.postid-310 .headerclass,
.postid-326 .headerclass,
.postid-404 .headerclass {
height: 250px;
background: #fff url(https://www.lifepathbydesign.net/wp-content/uploads/2016/02/BlogBanner.jpg);
width: 100%;
background-repeat: no-repeat;
background-position: center;
}
}