Then, when a mouse-over is detected on a link the according layer becomes visible. The trick behind these menus is to create all submenus as invisible layers. The most common use of this is to create menus that pop out (like the sub menus in the START menu on Windows). With dynamic HTML it is possible to change the visibility of a layer according to certain events. Why would anyone want to create an invisible layer? Well, imagine the possibilities it gives for adding pop-up menus and other cool effects on your pages. The techniques to create effects like that goes beyond the scope of pure CSS however, so for now we will just refer to DHTML (Dynamic HTML - a mix between JavaScript and CSS) for further explorations into that area.Ī final property is the visibility property that will allow you to create invisible layers. When the user clicks a link it will simply move the layer with the desired info on top rather than load a new page. You could create several 'pages' on top of each other - all on the same page. Very interesting possibilities arise from the fact that the z-index can be dynamically changed with JavaScript. Page layers 1.9.1 code#Try looking at the code example at the top of this page again, and see how we used the z-index to put LAYER 1 on top in the first example, while we had LAYER 2 on top in the second example. If the queen of hearts was at the top we'd say she had z-index:52. If the ace of spades was at the bottom we'd say it had z-index:1. The possibilities are endless - but in order to keep things simple, we will not dig into details about these dynamic HTML effects here. Other uses might be menus that pop out when a mouse-over is detected on a link. In fact this technique can be (and has been) used to create entire games. This means that it is possible to move things around on the screen even after the page has finished loading. In other words: at the bottom of your HTML code you can enter the code for a layer that is positioned at the top of the resulting page.īoth left and top properties can be dynamically changed You can enter both positive and negative values for these properties - thus it is possible to place content higher up and further to the left on the page than the logical position in the HTML code where the layer itself is defined. While the position property indicates the out spring of our coordinate system, the left and top properties defines the exact position of our layer. That is, if you add a relatively positioned layer in the middle of the page, then the position will be calculated from that exact spot in the middle of your page where it was added. If you define the position to be relative it will be relative to the position of the tag that carries the style. If you define the position to be absolute it will be calculated from the upper left corner of the page - unless the layer is defined inside another layer, in which case it will be calculated from the upper left corner of the parent layer. You can either position your layer calculated from the upper left corner(absolute) or calculated from the position where the layer itself is inserted (relative). The position itself is defined with the top and left properties.įinally, which layer is on top is defined with the z-index attribute. The position can be either absolute or relative. To create a layer all you need to do is assign the position attribute to your style.
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