A Joomla template is a set of files that contain the HTML and CSS code defining what your website will look like. HTML is the code used to build web pages and CSS is the code used to style them. You could say that HTML is the bricks and mortar of your site, whereas CSS provides the wallpaper and paint. Let's see how this works.
Without any CSS applied, your web browser would display a typical Joomla site as shown on the left-hand side in the next screenshot. Although the screenshots are too small for you to be able to discern the screen text, you'll notice that on the left-hand side just plain text and images are shown, with minimal styling. On the right-hand side, however, the same content is shown with CSS styles applied. Through CSS, the overall page layout and design is added:
Actually, a template contains more than pure HTML and CSS. After all, Joomla has to "know" where the dynamic content should be placed within the HTML page structure. That's why a template...