If you want your WordPress install to behave like Tumblr then Light Bright theme is just what your need. The theme comes with a dark background and big title font. Excerpt of the posts are displayed on the homepage. When you hover over the elements in the widgets, they do a little animation which looks cool. The theme comes with a sidebar widget area on the right side To behave like a Tumblr site the theme has options for multimedia integration. You can add links, photos, videos, and audio content along with the posts by creating custom posts types or taxonomies. Custom post types feature is what is used to make the them behave like a Tumblr site. The theme comes with 4 pre designed colors which can pick as per your own needs. You can also add Tumblr like widgets in the posts by adding plugins.