How to make a website look like a Windows Office application?

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I have a simple question which my Google searches were unable to find a decent answer to. I completely understand how to design websites with HTML, CSS and ColdFusion, but they always tend to look like a regular website with common navigation bar across the top, a sidebar, and then some main content.However I have also seen some software being used which looks exactly like a Windows Office application, even though it is being delivered through a browser. The ones I have seen are used in HR and CRM applications which are hosted in the cloud and accessed by companies through the internet. They look and feel exactly like Microsoft Outlook with the same rich functionality but are actually a website.So my questions is how do you go about making a site look like a Windows application? Where do you get all the nice icons, fonts, colour schemes, Javascript to put together a Windows 'theme'? Do you have to do everything from scratch yourself?