CartSella styling is global. You set the look of a surface once and every offer or upsell that renders on that surface picks it up. There is no per-offer colour picker, and there has not been one since styling moved to a single page. Find it at Settings → Storefront customization.
The Customize button inside an offer or upsell editor does not open a per-offer popup. It deep-links to this page, already on the surface that styles that item.
The Customize page with the surface rail, controls and live preview

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How the page works

The page has three columns:
  1. The surface rail on the left. One entry per stylable surface, grouped by where it appears.
  2. The controls in the middle. Colours, texts and layout numbers for the selected surface.
  3. The live preview on the right.
Above the preview there is a preview target selector on surfaces that have real records to preview. Picking one of your offers or upsells there changes what the preview shows, it does not change what you save. Whatever you edit always saves globally. Switching surface with unsaved changes prompts you to save first, so an edit you forgot about does not disappear.

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Surfaces

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General

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Offers (product page)

Product page card styling is per offer type, so a gift with purchase and a volume discount can look different if you want them to. Each type starts from a shared base style. The first time you edit one, it is seeded from that base, then it goes its own way. If you never touch a type, it keeps following the base, so existing stores see no change.

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Bundles

  • Standard Bundle
  • Build your bundle (app block)
Both style the product page card, alongside the offer types above.

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Upsells

  • You may also like. The full template editor for the product page upsell: layout, colours, texts, card style, cards per device.

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Cart

  • Cart upsell. The card layout and styling for the cart cross-sell.
  • Cart progress bar. Fill, track, text, success background and success text colours, plus the headline and success message. The milestones themselves live on the Progress bar page.
The cart upsell splits its settings. The card look is global here. The headline, max products, which surfaces it shows on, and its button colours live on the upsell itself, because those are content rather than style.

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Popups

  • Spotlight popup. The offers hub bubble and popup: bubble, popup background, popup text, accent, card background and border colours. The rest of the hub, including its content mode, badge, pages and countdown, is configured on the Offers hub page.
The boost popup is the exception among popups: its look is edited on the upsell itself, because it is offer-specific by design. See Boost popup.

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Pages

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Checkout and post-purchase

  • Thank you upsell. Style only. The template and its texts stay on the upsell.
Checkout upsells and post-purchase upsells have no global surface. Both render inside Shopify’s own checkout and post-purchase pages, which control the branding, so their whole configuration stays on the upsell.

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Campaigns

  • Campaign loader. The loading page shoppers briefly see when they open a campaign link: accent, text, muted text, card background, button text, plus the loading title, message and a logo URL.

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Use theme colours, or your own

Most surfaces start with Use theme colors turned on, which means CartSella inherits your store’s palette and the widgets read as native. Turn it off to expose the colour pickers. Text settings like a headline or a button label always apply, no matter which colour mode you are in.
Start with Brand, then click the button that pulls the palette from your published theme. It has the biggest visual effect for the least work, and it cascades into the defaults of every other surface.

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What is not on this page

Some things are styled where they are configured, because they have their own setup page with a preview:

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Translations

CartSella auto-translates the storefront text on your offers and announcement bars into your store’s other languages when you save. Only changed text is re-translated, so saving twice costs you nothing. See Languages and translations for exactly what is and is not covered.

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Tips

  • Prefer Use theme colors where it is offered. Widgets that match the theme feel like part of the store rather than an app bolted onto it.
  • Check the preview on a narrow window. Most shoppers are on a phone.
  • Save before you navigate away. The page warns you about unsaved changes, but it is easy to click through.