body {
  margin: 0;
  background-color: skyblue;
}
	
.left-nav {
  width: 200px;
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  padding: 6px;
  background-color: orange;
  box-sizing: border-box;
}

.main-container {
  position: absolute;
	left: 200px;
  top: 0;
  bottom: 0;
  right: 0;
  padding: 12px;
  overflow: scroll;
}