Moreover, modifying a mature site that contains many pages so as to use style sheets requires a lot of tedious work, nearly all of which can be avoided by designing a site so that it uses them from the outset. This time could probably be more profitably spent in learning to use CSS . It refers to the fact that CSS is designed in such a way that style information can be combined from various sources, and rules defined in one place can be overruled by ones given elsewhere. This is briefly discussed in a later page of this guide. By contrast, web pages often have almost no detectable margins.
Books normally have black print on white paper.
However, it is also a matter of legibility, and even very expensive books usually have mainly black text against a white background even if they have colour illustrations. Another technique when printing on sheets that are large compared with typical books is to increase the amount of white space between lines. On the web, however, lines often contain as many as 100 characters per line and HTML offers no simple way to increase the spacing between lines. If all of these problems could be solved without the use of style sheets the case for describing them in an elementary guide would be very weak. In fact, as we shall now see, creating margins requires improper use of HTML tags, creating a white background is quite easy, and changing the space between lines cannot be done at all in a satisfactory way.