Shopify let's you do some customiztion on the Checkout page. Shopify Plus plan gives you access to the checkout file to do custom work. It's also possible to add countdown timer and other content on the checkout page using code that is added to Additional Google Analytics field in your online store preferences. However, this is not a feature that is designed by Shopify, so we do not recommend using it. Use these settings instead:
1. Navigate to Checkout settings (in the bottom of theme settings).
2. On Banner you can add a custom image at the top of your checkout page.
3. At logo settings you can add your logo, edit it's positiong and size.
4. At Main Content Area you can edit the left side of your checkout page. Add an image, or edit the background color. You can customize the Form fields to be white or transparent.
5. On Order Summary you can edit the right side of your checkout page. Add an image or edit the background color.
6. Lastly, you can edit the Typography and colors on your checkout page.