When you collect information from people through a form, applying some kind of validation is a must. Failing to do so could lead to lost customers, junk data in your database or even security exploits of your website. Historically, building form validation has been a pain. On the server side, this is made easier by full stack frameworks which handle it for you, but on the client you often end up with JavaScript libraries that take a lot of effort to integrate.
Thankfully, HTML5 gives us a number of features that can handle most of your validation needs. Forms in HTML5 now have built-in support for validation through the use of special attributes and new input types, and give you a lot of control over styling with CSS.
http://tutorialzine.com/2014/12/quick-tip-easy-form-validation-with-html5/