What Shadow DOM Does
When the Render Cart in Shadow DOM setting is turned on, Upcart creates a self-contained space that keeps its styles and scripts separate from the rest of your store.
This means:
Your theme’s global CSS can’t override Upcart’s design.
Upcart’s styling also won’t interfere with your theme.
The cart stays consistent across different devices and themes.
You can think of Shadow DOM as a “protective bubble” around your cart that helps it look and work the way it’s meant to.
How this happens
Shopify and third party themes often come with global CSS and JavaScript that can unintentionally affect how Upcart looks or behaves.
The Render Cart in Shadow DOM setting helps prevent these conflicts by isolating Upcart’s cart drawer inside its own protected environment. When enabled, Shadow DOM keeps your cart design and layout consistent, regardless of theme updates or custom code changes.
However, if your theme or third-party app needs direct access to cart elements, this isolation can sometimes create integration challenges.
Technical Considerations
If you or a developer need to modify elements within Upcart using JavaScript, it’s important to use the right document references:
Use
upcartDocumentOfShadowRootwhen targeting elements inside Upcart.Use
documentwhen targeting elements outside of Upcart (for example, your Shopify theme’s header or footer).
Even though the Shadow DOM is isolated, Upcart still provides ways to interact with your theme and other apps through its Public API and helper functions.
Troubleshooting and Limitations
In most cases, enabling Shadow DOM will fix CSS and layout conflicts automatically.
However, there can always be some scenarios where you may still experience issues:
Pricing apps: If another app needs to directly modify prices or checkout behavior inside the cart, Shadow DOM can make that difficult since it hides Upcart’s internal structure from external scripts.
Theme-level JavaScript: Custom scripts that use
document.querySelector()may not find cart elements while Shadow DOM is enabled.
If you need to test your store's behaviour for these integrations, you can always temporarily disable Shadow DOM in Upcart → Settings → Advanced Settings.