We had our Sitecore developer create a template that allows for the insertion of HTML, CSS <link>s and <script> tags. Each of these has a separate input textbox in the template. It looks like this:
And that's it!
Hi Abhijeet, you will need to ask your Sitecore developer to implement a Sitecore item template like the one in the screen-shot that I've included in the answer. I was not in the team that created the template, so I don't know much about the implementation. If you have any specific questions, please feel free to ask and I will endeavour to answer them.