This is another late answer but i figured out a fairly simple way of placing the "bar" text in between the four squares. Here are the changes i made; In the bar section i wrapped the "bar" text within a center and div tags.
<header><center><div class="bar">bar</div></center></header>
And in the CSS section i created a "bar" class which is used in the div tag above. After adding this the bar text was centered between the four colored blocks.
.bar{
position: relative;
}