Internet Explorer says, "TL;DR"

Internet Explorer has limitations to the amount of CSS that can be parsed for a webpage. But what are the limits and are you at risk?

Problem space

To reduce the number of HTTP calls and increase the performance of a website, developers can compile all of a sites CSS into a single file and serve it once. This can result in a large number of rules and selectors in a single file.

Before taking this performance optimisation approach, you should be aware that Internet Explorer has limits on the amount of CSS that it will process and will ignore any extra rules in order to limit memory usage as it's TL;DR (too long, didn't read).


The following are excerpts from Stylesheet Limits in Internet Explorer

  • A sheet may contain up to 4095 rules
  • A sheet may @import up to 31 sheets
  • @import nesting supports up to 4 levels deep

Internet Explorer 10 platform preview #2 significantly increases the limitations (in any browser or document mode).

  • A sheet may contain up to 65534 rules
  • A document may use up to 4095 stylesheets
  • @import nesting is limited to 4095 levels (due to the 4095 stylesheet limit)


The following URLs contain practical examples of the issue. You will need to use Internet Explorer to view the results.

Risk Analysis

To find out if your CSS files are at risk in Internet Explorer, you can use this useful tool from to count the number of selectors in a CSS file.

Testing & QA

Regardless of which browser or document mode you use Internet Explorer 10 cannot be used to test this browser issue as it will always use its higher limits.

To simulate this limitation, you can use a virtual machine with Internet Explorer pre-installed. This allows you to check your site in older browsers and identify the visual problems.