Toolbar Flickers while scrolling page

I have some problem with toolbar in my project. on some pages when I scropl the page the toolbar starts flickering. I am using this style for toolbar class:

.toolbar {
overflow: visible;
background-color: @bc-bg;
height: @headerbar-height;
color: @white;
vertical-align: middle;
line-height: 38px;
position: fixed;
z-index: 99;
padding: 0;
width: 100%;