Remove unused css code

## What is the problem?
* The production build css files are of large sizes(over 700kb). as per the chrome's code coverage report, over 70% of the css code in the file are not used

## What is the impact?
* The large size files affects the initial loading of the app.

## Proposed solution
* Use webpack plugins like purgecss to remove unwanted css codes
* Implement lazy loading