There are no set rules of Web design just yet. Only those that are already adapted from the printing business. Remember - some rules can be bent, others can be broken. You have to know them first, to do so, however. When talking beauty, one must differ art from design.
Art is the visual expression of feelings in any medium.
Design is based on rules, not feelings alone. Accepting this, the rules of design, are based on traits of beauty that repeat themselves. They are based on experience of what works and what does not. Contrast Contrast, is one rule of design. In Buddhism, recommended is the golden middle way, the perfect combination of these contrasts.