C++ (Qt)
QMainWindow::separator::vertical {
     background :qlineargradient(spread:pad, x1:0.993909, y1:0.455, x2:0, y2:0.511, stop:0 rgba(172, 172, 172, 255), stop:1 rgba(255, 255, 255, 255));
     width: 5px; /* when vertical */
     height: 5px; /* when horizontal */
 
     border-radius: 2px;
 
 }
 
 QMainWindow::separator:hover::vertical {
     background:qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(102, 102, 102, 255), stop:1 rgba(255, 255, 255, 255));
 }
 
QMainWindow::separator::horizontal {
     background :qlineargradient(spread:pad, x1:0.494, y1:1, x2:0.483, y2:0.0166818, stop:0 rgba(172, 172, 172, 255), stop:1 rgba(255, 255, 255, 255));
     width: 5px; /* when vertical */
     height: 5px; /* when horizontal */
 
     border-radius: 2px;
 
 }
 
 QMainWindow::separator:hover::horizontal{
     background:qlineargradient(spread:pad, x1:0.5, y1:0.017, x2:0.5, y2:1, stop:0 rgba(102, 102, 102, 255), stop:1 rgba(255, 255, 255, 255));
 }
самые оптимальные настройки