The Custom Code section in the Construction theme Customizer contains 3 options. Navigate to Appearance → Customize → Theme Options → Custom Code to access these settings.

Options

• Custom CSS (Textarea) — Add custom CSS to your theme.
• Header Code (Textarea) — Custom code for the header.
• Footer Code (Textarea) — Custom code before closing body tag.

After making changes, click Publish at the top of the Customizer to save your settings.