Polymer is an open source java-script library for building web applications using web components. Developed by Google developers and contributors on GitHub.
Modern design are implemented in the project using Google material design principles.
for more informations : Polymer Project
since the beginning of times humans used to develop web sites and web applications. but it was a mess, well it still is but less than before...imagine yourself in a world where you develop something that you'll only use once in your life time, imagine than that you have to redo your code all your life long.... better kill yourself now X). so let's think reusability ?
Web components are the solution.
it's a set of features currently added by the W3C to the html and the dom specifications it allows the creation of reusable widgets and components in web docuemnt and web applications.
in short, it consists of 4 main features which can be used separately or all together :
let's take a look at a modern web app