This article explains how to create a persistent "Catfish" ad banner that remains visible at the bottom of a webpage even when scrolling. The technique uses a combination of CSS and JavaScript, with special handling for Internet Explorer.

Key Concepts:

• Persistent Bottom Banner: The core functionality is a DIV element positioned at the bottom of the page using CSS (position: fixed).
• Cross-Browser Compatibility: The initial CSS-only approach, using position: fixed, doesn't work in older versions of Internet Explorer. The solution involves conditional comments and DOM manipulation to add a wrapper DIV (div#zip) for IE only. This wrapper uses position: absolute for the banner and overflow: auto to manage scrolling within the wrapper.
• IE-Specific Handling: A custom JavaScript function (wrapFish) dynamically injects the wrapper DIV into the IE DOM, ensuring compatibility without impacting other browsers.
• Conditional Comments: These comments allow for browser-specific CSS and JavaScript inclusion. This ensures that only IE receives the extra markup needed for the fix.
• Efficient Markup: The extra DIV and associated styles are only added for Internet Explorer, avoiding unnecessary bloat for other browsers.

Code Snippets:

The following code snippets illustrate the CSS and JavaScript used. Note that this is a simplified version for demonstration.

catfish.css:

#catfish {
  position: fixed;
  bottom: 0;
  background: transparent url(images/catfish-tile.gif) repeat-x left bottom;
  padding: 0;
  height: 79px; /* includes transparent part */
  cursor: pointer;
  margin: 0;
  width: 100%;
}

html {
  padding: 0 0 58px 0; /* 58px = height of the opaque part of the Catfish */
}

IEhack.css:

div#zip {
  width: 100%;
  padding: 0;
  margin: 0;
  height: 100%;
  overflow: auto;
  position: relative;
}

catfish.js:

function wrapFish() {
  // ... (JavaScript code to wrap the content in div#zip for IE) ...
}

Conditional Comments (Example):

<!--[if lte IE 6]>
  <link rel="stylesheet" type="text/css" href="IEhack.css">
  
  
<![endif]-->

This approach ensures a consistent user experience across browsers while minimizing unnecessary code. Further refinements, such as conditional banner selection and placement control, would enhance the functionality.

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