When you consider use modern browser features, like advanced HTML5 and CSS3 selectors you need to be sure that the target browsers expected to visit the site actually supports the features. The website caniuse.com gives you an overview of which browser versions supports a given feature.
That is nice, but this blog post How to Use Your Own Web Statistics at caniuse.com takes it a step further: You can import Google Analytics data to caniuse.com from your sites and get the relevant “Can I Use” information from Your site! That is so cool!
Read the blog post above, or simply visit caniuse.com, click “import stats”, authenticate using Google Account and choose which site to use statistics from! You should turn off pop-up blocking, as the Google Account authentication will pop-up in a new window.