As mentioned earlier, transitions are a CSS3 property. All modern (major) browsers support them: Chrome, Firefox, Safari, Internet Explorer, and Edge. Older browsers, such as IE9 and below, don't support them. They still get the hover state, but it will be abrupt without any transition. This isn't a problem as transitions typically aren't a core feature of your website, but more of an added experience level. Still, they are CSS3, and we can get a little more mileage out of them by including the vendor prefixed versions. Traditionally, the -webkit- prefix was used for Safari and Chrome; -moz- was used for Firefox and -o- for Opera. However, Firefox and Opera also now use -webkit-, so technically you don't need -moz- and -o- ...
Vendor prefixes
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