Greetings, Prof Aravind,
The CTAT components are, initially, empty <div> elements with CTAT-specific class attributes that you arrange on your student interface's HTML. The CTAT runtime code in ctat.min.js (that you include with a <script> tag in your HTML <head>) reads the document once the page is loaded and, for each <div> with a CTAT class (CTATTextInput, CTATButton, etc), invokes constructor code that dynamically adds actual HTML components (<input>, <button>, ...) as child elements of the original <div>s.
Hence in addition to the CSS files, you'll need to ensure that ctat.min.js is included and initTutor() is called on or after the onload event. See this MDN page
for info re: onload. Thanks!