In: Computer Science
Latest version of CSS.
From the official release notes of css, there is no CSS Level 4 or beyond. Independent modules can reach level 4 or beyond. That is CSS, as the language has the latest level 3. For CSS, there's no version, we call it level. So, the latest level (version) is CSS3.
Browser requirement
Almost all modern browsers support css3. Most of the css properties are supported by modern browsers such as chrome, safari, firefox, opera.etc. There are certain prefixes like -webkit-, -moz-, -ms- which are required to be prefixed to some standard tags.
For instance, consider the standard syntax transform: rotate(20deg);
/* Standard syntax */
transform: rotate(20deg);
/* IE 9 */
-ms-transform: rotate(20deg);
/* Safari */
-webkit-transform: rotate(20deg);
For a list of full reference, visit css3 browser support page on w3schools. (search google to get the page. I can't paste external link here)
Two browsers that support css3 : Chrome, Firefox
Designing for CSS3
To design for css3, you simply need to use the css properties and their values as specified in the css3 documentation.
Higher levels of CSS are built on top of lower levels by adding functionality or replacing parts of the lower specifications. So, support for css3 means supporting the lower levels also.
Feel free to comment if you need more clarity. Kindly upvote, if you are satisfied with the answer.