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CSS-Only Box Shading Technique

By jfparadis
Jun. 1, 2010

Introduction

Here is a fun technique to add shading to your web pages using only CSS with PNG images, without using JavaScript, Flash, server-side scripting, or Photoshop, and remain totally independent from colors and textures.

Try it here.

Background

Most shading techniques suffer the drawback of the core technology they use:

  1. Photoshop: images must be individually styled for each pattern combination
  2. Javascript: CPU intensive

The main issue with Photoshop techniques comes from the time spent creating images, and from the complexity of the code to keep tack of them. For each color/teture combination, 8 images (4 corners and 4 edges) are required.

One technique called “sliding door” reduces these elements to 6, but requires larger images:

A new approach

Our technique is based on the same basic idea used in 3D rendering engines which separate textures from shading. Here is an example showing the difference between shades + textures, and shades only:

The first step is to create the shade PND images. Simply use a mask to hide the box content (see the included files):

To optimize this technique, we can reduce the top and bottom elements’ width, and the left and right elements’ height to one pixel.

To use on a web page, we simply create a box element normally, wrap it in a “shade” container and add the required elements.

For the most complex case:



 

  
 


 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

For fixed-with boxes, such as page containers, we only require 3 elements (top, center, and bottom):



 

  
 


 
 

 
 

 
 

Likewise, fixed-height boxed such as title containers only require 3 elements (left, center, and right):



 

  
 


 
 

 
 

 
 

You do not have to create the shade element, you can just apply the shade class to an existing one. The only purpose of the shade element is to serve as a wrapper and an anchor for absolute positioning.

Fore each shading element, we define a negative margin (here 10 px) to accommodate the shade and use a negative z-positioning to place the shade below the content of the box.

.shade {
 position:relative;
}
.shade .TL, .shade .T, .shade .TR,
.shade .L, .shade .C, .shade .R,
.shade .BL, .shade .B, .shade .TB {
 position:absolute;
 z-index: -1;
 top:-10px;
 left:-10px;
 right:-10px;
 bottom:-10px;
}
.shade .TL {
 background: url(s/tl.png) no-repeat left top;
}
...

As always, the best way to fully understand a technique is to look at a demo, or to download the source. Next time, we will look at a Drupal theme which implements this technique.

Cheers!

JF

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