If you are a Shopify Plus customer, you have the ability to fully customize the layout of the checkout page using the checkout.liquid and checkout.scss.liquid files in the theme editor section of your Shopify store's admin panel.
If you’re not a Shopify Plus store, then you’re more limited in the checkout customizations you can make. However, you can still edit elements like your logo, your form length, page colors, text and more.
