You know how it works: you delevelop a nice site and after finishing the client tells you that he cant manage or even see it. Because they still rely on IE8 for some reason or they cant update their browser because they have no admin rights on their machine.
Here is a collection of links that might point you into the right direction. As there is not "the one" solution for every problem on the topic, you will have to find out for yourself what will suite your situation.
- Making older browsers understand HTML5 https://en.wikipedia.org/wiki/HTML5_Shiv
- Testing for available HTML5 features: https://en.wikipedia.org/wiki/Modernizr
Be strong, you'll find a way :)