Avoid CSS Expressions (Deprecated)

CSS expressions were a way to set various CSS properties, like the width of page, specific page background color and border, and many other options. CSS expressions have been subsequently removed from all major browsers (except Internet Explorer versions 6 and 7), but back in the early 2000’s when they were released with Internet Explorer 5, they were a way for web development teams to help configure, customize, and arrange pages that tied together the look and feel of the website to the company’s business or brand identity.

While CSS expressions were a great feature to connect the user to the brand through a website, all these dynamic elements consisted of JavaScript, which as you are aware, affects rendering time as the browser would need to evaluate each one every time an event, like scrolling, page resize, etc., was triggered. It was reasons like these that eventually lead to CSS expressions being removed by the time Internet Explorer version 8 was launched. Since then, the recommendation from Google PageSpeed has been to avoid them at all costs and to use standard CSS expressions, or simply just use JavaScript code only, which all browsers support.