Tumblr is a blog service which allows users to change their theme, more commonly known as an HTML template. You can update your theme by either custom coding it, finding a free one, or purchasing one.
To check out my blog which I hand coded, visit gyrospring.tumblr.com
To learn more about creating a Tumblr theme, visit Creating a custom HTML theme | Tumblr.
While I was designing a theme I came to the conclusion that I did not want to use the Likes and Reblog features. The main reason, which took me an entire day to figure out, was that visitors can be non-Tumblr users, so what's the point of the buttons to those people? For all I know 99 percent of my visitors may not even know what Tumblr is.