Is it possible to have a custom look and feel for the tabs in salesforce? If I have to create a visualforce page, I just want to change the look and feel of the Tabs and pages but the functionality of the page should be the same.
Unfortunately there is no officially supported way to change the look&feel of the tabs in salesforce. You can only select one of the colors and icons you have already seen in the tab wizard. That's it.
What you could do for your specific visualforce page is to create it without the salesforce default style and header and create the entire page on your own like this:
<apex:page sidebar="false" showHeader="false" standardStylesheets="false" applyHtmlTag="false"> <!-- PUT YOUR ENTIRE MARKUP HERE --> </apex:page>
But then you also have to create your own kind of navigation as replacement of the tabs.
An not officially supported way would be to create the page with showHeader="true" and sidebar="true" and override some CSS to tweak the look&feel. But this would only apply to your single custom page. On other pages in Salesforce, the tab would look like default again.
Due to my knowledge, none of the above workarounds is good enough in that use case. In order to get a consistent look&feel, you should either stick with the default look&feel or you would have to create your entire app using ONLY visualforce pages containing your own navigation (tab replacement) and entirely your own html/css.