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Debugging CSS

By Renoir Boulanger


This article lists utilities to help analyze situations where a CSS style we think should be applied is not.

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Methods for debugging CSS are essential, since CSS errors will not output any error message indicating the source of the issue at hand.

Avoiding problems in the first place

Cross browser Idiosyncrasies

As mentioned in previous tutorials Web Browsers come with inbuilt CSS. This default CSS may differ between browsers and hence when viewing a site, unless the site CSS cancels out the browser’s CSS there is a chance that the page is displayed differently across browsers, which most often than not it is undesirable.

This problem is avoided by normalizing the browser. This is done by using a set of CSS rules to cancel the web browser default CSS before applying custom CSS. There exist a couple of CSS normalizing files on the net freely available.

CSS to debug CSS

One of the things that could help in identifying a layout issue or perhaps some complex structure like a CSS based menu one would want to see what is really going on in terms of boxes.

  outline:1px red solid;

Using the above will display an outline around each element on the page indicating the structure, which could help in identifying where certain problems are.

Isolate the issue

If the problem is in a fully blown site with plenty of HTML/CSS, start commenting out the HTML and CSS rules and try to isolate the issue and perhaps even replicate it and try to find the offending rules.

WebBrowser tools

At the time of writing Google Chrome/Mozilla Firefox and Internet Explorer come with inbuilt developer tools that could help with debugging. These tools allow to inspect elements and view the CSS applied on them. Furthermore one could disable rules, remove properties, add rules and add properties and view the changes in the browser.


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See also

External resources