Internet Explorer (IE) 8 was the last version of Microsoft's Internet Explorer browser before they began development on Edge. In order to improve its performance and security, Microsoft implemented a number of changes to the browser inIE8.css, a CSS file that was used to style the browser's elements. This file contained a number of changes to the browser's behavior and appearance, including changes to the way that elements were displayed and structured.

One of the main changes inIE8.css was the introduction of the "width" property, which allowed developers to specify the width of elements in percentage values. This change made it easier to style elements in a way that was specific to a particular device or screen size, rather than based on the browser's default width.

Another change inIE8.css was the introduction of the "max-width" property, which allowed developers to specify a maximum width for elements. This property was used to prevent elements from being wider than their maximum width, which could improve the performance and security of the browser.

In addition to these changes,IE8.css also contained a number of other features and changes to the browser's behavior, such as the introduction of support for CSS3D effects and the addition of the "border-radius" property.

Overall,IE8.css was a significant change to the browser's behavior and appearance, as it made it easier to style elements in a way that was specific to a particular device or screen size. The introduction of the "width" property and the "max-width" property were two key changes inIE8.css that helped to improve the performance and security of the browser.