What are the dominant themes/preoccupation of late Victorian and Edwardian fiction?

As in any era, the literature of the late Victorian and Edwardian periods reflected social concerns of the time. A general consciousness of the change in the century—the "fin de siecle"—lent the literature of this period a sense of anxiety, with authors questioning the structure of their society and of their literature itself. In the early Edwardian period, this was expressed through the emergence of Modernism, the Bloomsbury Group and their challenges to political norms (E.M. Forster, the Sitwells, etc). Because you have listed this question in the "Oscar Wilde" category, however, I will focus on how this theme is represented in the literature of Wilde and his late Victorian contemporaries.
Wilde's only novel, The Portrait of Dorian Gray, covers themes that can be found in several other contemporary works: namely, Bram Stoker's Dracula and R.L. Stephenson's Dr Jekyll and Mr Hyde, among others. These novels—part of the Gothic Revival—cover themes of conflicted identity and reflect the fear that society is not what it appears to be. The theme of appearance vs reality expresses itself in all these works in the fear that a benign exterior conceals a repulsive interior. This is another way of commenting on the ugliness of a society that pretends to be genteel. As the 20th century moved on, writers began to examine social ugliness, division, and poverty in ways that were less and less veiled. In the late Victorian period, however, the theme of the supernatural (or supposed supernatural, as in Collins' The Moonstone) was often used to convey these other more realist concerns.