Truly Minimal

Hi guys i am trying to modify truly minimal so the sidebar appears for longer like at 700px width. I managed to resize the sidebar to what i wanted but the problem is the sidebar drops below the content at around 800px. This is the code i added in custom css.

@media only screen and (min-width : 700px) {
.sidebar-left .site-content {
margin: auto auto auto 140px;
}
}