USE HTML5 / CSS3 / JS / JQUERY elements to develop the finished version of your project using only ONE single CSS file for all the pages. The menu needs to be unified, and MUST NOT change from page to page.
You may be tempted to use JQuery includes in your final site: use it ONLY ON INDIVIDUAL pages, NOT the entire site. I understand it makes sense to create a Template and load the dynamic content into it, but in reality you would have to preload every single asset in your site for it to be efficient. It can be a total nightmare, and completely kill the experience for the users. This is the goal of Server Side programming, using PHP, but you would have to have your own personal server for this to be implemented. This is the subject of something you can learn in an independent project in future semesters, if you are interested in databases and dynamic web development.
Consider this as the finished project for your client: it may be in the form of a web site or web app, but you can emulate the App look.