Let's give this a go. Add the following to wherever your other blog CSS is.
/* begin blog hidden sidebar reclaim space */
.collection-type-blog #page {
display : flex;
}
.collection-type-blog.blog-sidebar-display-right .article-list,
.collection-type-blog.blog-sidebar-display-right .article-wrapper
{
margin-right : auto;
width : 100%;
}
.collection-type-blog.blog-sidebar-display-right #sidebar {
position : unset;
margin-left : 50px;
}
/* end blog hidden sidebar reclaim space */
Let us know how it goes.