#footer, #sidebar-header {
   position: relative;
   background: #f5f5f5;
}
#footer:before, #footer:after, #sidebar-header:before, #sidebar-header:after {
   content: "";
   position: absolute;
   background: #f5f5f5;  /* Match the background */
   top: 0;
   bottom: 0;
   width: 9999px;   /* some huge width */
}
#footer:before, #sidebar-header:before {
   right: 100%;
}
#footer:after, #sidebar-header:after {
   left: 100%;
}