<!DOCTYPE html>
<style>
    #block1 {
        width: 200px;
        height: 100px;
        border: 4px solid darkgreen;
        background-color: green;
    }
    #block2 {
        width: 100px;
        height: 50px;
        border: 4px solid darkred;
        background-color: red;
        z-index: 200;
        position: relative;
        left: 50px;
        top: 25px;
    }
    #block3 {
        z-index: 500;
        position: relative;
    }
</style>
<div>This tests that an element with a positive z-index appears behind the full screen element.
     After entering full screen mode, the green box should not be obscured by the red box.
     Click <button>go full screen</button> to run the test.</div>
<div id="block2"></div>
<div id="block3">
    <div id="block1"></div>
</div>
<div>END OF TEST</div>