Design your own blog.
The CSS Editor allows the blog administrator to modify the visual style of the blog. While the theme’s HTML cannot be modified, Custom CSS gives you the power to make your own design. If you haven’t found your ideal theme on WordPress.com, Custom CSS is for you. If you’d like someone else to design a new CSS theme for your blog take a look at 99designs.
The CSS Editor can be found under Edit CSS in the Appearance menu of your dashboard. It consists of a blank area for typing and two buttons:
You can edit your CSS and preview the changes without affecting the public view of the blog while experimenting with new styles. In order to save your CSS changes and publish them to your blog, you need to purchase the Custom CSS upgrade. You can edit and save your stylesheet as often as you like; you can use uploaded images as backgrounds; you can modify an existing theme or start from scratch with the Sandbox theme. There is a CSS Customization forum where you can ask for help or give assistance to others.
Purchasing the upgrade entitles you to use Custom CSS on one blog for one year.