version - what is style.css?ver=1 tag?

Question

I found out that some websites use css tag like style.css?ver=1. What is this?

What is purpose of ?ver=1?

How do I do it in code?

Answer 1

To avoid caching of CSS.
If the website updates their CSS they update the ver to a higher number, therefore browser is forced to get a new file and not use cached previous version.
Otherwise a browser may get a new HTML code and old CSS and some elements of the website may look broken.