100% Height Sidebar

Say you want the background and/or border of the sidebar to extend the full height of the page…

.container { 
  overflow: hidden; 
  .... 
} 
#sidebar { 
  margin-bottom: -5000px; 
  padding-bottom: 5000px; 
  .... 
}

.container {

overflow: hidden;

....

}

#sidebar {

margin-bottom: -5000px;

padding-bottom: 5000px;

....

}