How can I make DIV 100% height of browser without vertical scrolling of header

Question

Both the left and right panels have a height of 100%, but since the Header div takes up X amount of space, there is some vertical scrolling in the window th

Answer 1

Use viewports. Browsers now support giving height a percentage of page height. Drop the 100 down to 80 if you've got a header taking up space.

div {
    height:100vh;
}