One of Superstore’s advantages is found in the Custom styles and scripts portion of the Theme settings. Use the fields provided to add custom code snippets with ease.
Access the custom styles and scripts settings
Go to Customize > Theme settings > Custom styles and scripts
Add custom styling adjustments
Use the CSS (Cascading Style Sheet) field to add custom codes that influence the styling of the theme.
All code added to this field must be arranged in correct CSS formatting. For an introduction to this, check out this guide from w3schools.com
Add custom scripts
Use the two JavaScript fields to add custom codes for customizations, apps, etc. There are two fields provided, Standard and Critical.
The difference between them relates to the priority of execution. In other words, when the storefront is loading, using these fields determine whether the JavaScript is loaded first (Critical) or after other components (Standard).
For an introduction to JavaScript, check out this guide from w3schools.com