It's possible to override knowledgebase styling by following these steps:
- Go to Settings -> Styles and create a custom style
- Navigate to your public knowledgebase and use browser tools to identify the elements you wish to style
- Enter these style overrides into the custom stylesheet you created in step 1
- Go to Settings -> Company Settings
- Select the 'Styling' tab and set the Knowledgebase Styling Overrides value to the name of the new style you created in step 1
- Refresh your public knowledgebase each time you make a change to the CSS to test your work
- Repeat until you're happy with the outcome