You want to pull global styling applied to your email template (background color, borders, etc.) into the footer used in campaigns. To accomplish this, you will need to edit your footer in Account Management.
1. Navigate to Settings > Account Management
2. Locate and click 'Footers'
3. Hover over footer and click 'Edit'
4. You will be dropped into 1: Setup. Either click on '2: Design' (top, left) or click 'Save and Next' (top, right) to move into Design.
5. Click 'STYLE' (right)
6. Locate and check 'Inherit styling from email' under Appearance
7. Click 'Save'.