One of my templates has a responsive.css file....
Within it is code like this-
@media (min-width: 421px) and (max-width: 680px) {
.topMenu table { width:450px; margin:auto;}
#sys_main_logo { width:450px; }
#sys_main_content { width:450px; margin:auto;}
#sys_ml { width:450px; }
#sys_mc_wrapper { width:450px; margin:auto;}
#page_column_1 { min-width:450px; max-width:450px; margin-left: 5px;}
#page_column_2 { min-width:450px; max-width:450px; margin-left: -5px;}
#sys_main_menu { max-width:450px; }
.sys_sub_menu { width:450px;}
#sys_mm { max-width:450px;}
}
@media (max-width: 420px) {
.topMenu table { width:275px; margin:auto;}
#sys_main_logo { width:275px; }
#sys_main_content { width:275px; margin:auto;}
#sys_ml { width:275px; }
#sys_mc_wrapper { width:275px; margin:auto;}
#page_column_1 { max-width:275px; margin-left: 5px;}
#page_column_2 { max-width:275px; margin-left: -5px; }
#sys_main_menu { max-width:275px;}
.sys_sub_menu { width:275px;}
#sys_mm { max-width:275px;}
.sys_breadcrumb { max-width:275px; margin:auto; margin-top:8px;}
.sys_copyright { max-width:275px; margin:auto; margin-top:8px;}
.sys-service-menu-wrp {position: relative; margin-bottom:10px; top: 10px;right: auto; width:205px; margin-left:auto; margin-right:auto;}
#sys_search {position: relative; top: auto; right: auto; left: auto; margin-bottom:10px; }
#sys_ml_wrapper {text-align: center;}
}
As GG said- You would need to add in "display: none;" (for whatever you are trying to hide) into one of the correct sections or screen sizes you're trying to apply this configuration to.
Mind you, your template may be different.