It really depends on your website's complexity. It should be fine for the websites offering few services. For a complex site, I would recommend using PHP.
HTML is required for all websites. Nothing else is needed for a simple site. For more complex sites you have many options to supplement the HTML.
HTML and CSS is important for making website. but you also use the ajax,java script and jquery making a good websites.Just check the site Look Beyond Resumes,you definitely find the good idea about the designing.
html and css both have its importance,a website is incomplete without both of these you may use any other language like php with it.