I'm assuming you're asking about CSS in combination with HTML, since otherwise you can't really get any styling into an HTML document. There are plenty of differences — though don't forget about the many similarities as well.
(La)TeX has a very good knowledge of typesetting requirements and media.
- (La)TeX will justify text, automatically hyphenate, provide proper spacing, and other typesetting features. (You can use XeTeX for even more typographical features.) The default
article class has the text width optimized for readability. Most browsers don't have this type of functionality, and with HTML/CSS you have to manually specify sizes.
- (La)TeX will paginate content and you can set up different page styles based on left/right pages for physical publishing purposes. HTML has no intrinsic knowledge of "page layout" in terms of a single physical page of paper. You can specify print-specific layouts with CSS, but pagination is not trivial.
(La)TeX and HTML have different positioning systems.
- Some things are similar, like the layout of text in regions, and fine-grained position adjustment, but one primary way of positioning stuff with CSS is "floats" which allow much more control over positioning than LaTeX floats. At the same time,
\hfill doesn't really have a CSS equivalent unless you use tables.
Cascading Style Sheets are cascading.
- With CSS you can specify styles that are based on a hierarchy of elements on the page, rather than LaTeX's scoped inline style commands. Elements automatically inherit most of the styles from their parent but can be overridden based on any number of factors.
HTML documents are live and responsive.
@media queries that let you provide different layouts for different target media (everything from screens and printers to screen readers and 3D glasses — anything that any client uses), as well as different viewport sizes.
HTML is most often written with the expectation that it will be used in a browser, so it is very common to take advantages of features like the
Browsers get to make up their own features!