Use branding as an option to change the look and feel of the theme. Branding of theme can be done in many ways:
Changing the Name: Set the name of the Help Center. For example, your customers might be used to calling your content Support, Help and Tutorials, or Documentation. The name doesn't affect the URL of the Help Center.
Changing the Logo: Change the default logo image displayed in the header. The recommended image size is 200px by 50px. If the width or height of the image exceeds the recommended size, the image is scaled down to keep the aspect ratio constant.
Changing the Favicon: A favicon is a small image that appears on a browser tab or next to the URL in the browser's address bar. For best results, make sure the favicon is a square image. The image is scaled to fit the display dimensions.
Adding Banner: While there is not an option to add a custom image banner to theme from within the code-editor, it is possible to do so with Custom CSS. By adding a few snippets of CSS, you can override the existing banner with a banner of your choice.
Add Background image: Add background image to your help center to enhance the existing look and feel of your help desk. Background images, just as the name implies, are part of the BACKGROUND of a theme, not part of the actual content. The most common place to add a background image is in Help Center's CSS.
Changing Colors and web fonts: Using custom fonts is a great way to add a bit of simple flair to your web portal. You can use Google Web Fonts to change the header title and forum title in Zendesk.
How to do it
In the Help Center, click Customize design in the tools panel on the lower-right side of the page.
The Help Center switches to Preview mode.
Set the options in the Appearance, Branding, or Mobile Branding panels in the sidebar.
When you make a change, the page refreshes to let you preview it on the page. Changes don't take effect until you click Publish changes at the top of the sidebar. Most of the options are self-explanatory.
Click Close to leave Preview mode.