Layers in CSS
You modify the menu_system.css style sheet in two key areas. The first modification involved controlling the layering of the JT’s logo, so that the JT’s logo is always on top. To do this, you apply a z-index: 1; declaration to the rule for the JT’s logo. This demonstrates that an integer provided to the z-index property, which specifies layering by providing a number, takes precedence over the auto z-index. This means that the auto z-index is determined first, and then elements with a numbered z-index appear above those with an auto z-index. In this scenario, this eliminates the need to explicitly specify a z-index for any of the other elements.