[Bug] `<shopify-account>` crashes WebKit on iOS 16 (EXC_BAD_ACCESS in RenderThemeIOS::systemColor due to Relative Color Syntax)

Description:
On iOS/iPadOS 16.x devices, loading a storefront with <shopify-account> enabled causes an immediate WebContent process crash (EXC_BAD_ACCESS / SIGSEGV at 0x8).

Root Cause:
The Shadow DOM styles injected by <shopify-account> include CSS Relative Color Syntax with var() references on pseudo-elements:

.account-button__avatar::before {
  box-shadow: 0 4px 4px rgba(from var(--shopify-account-signed-in-avatar-color-background) r g b / .12);
}

On iOS 16 WebKit engines, evaluating dynamic CSS variables inside relative color expressions on pseudo-elements dereferences a null pointer in WebCore::RenderThemeIOS::systemColor.

Stack Trace from .ips Crash Log:

• WebCore::RenderThemeIOS::systemColor
• WebCore::CSSPropertyParserHelpers::consumeOriginColorRaw
• WebCore::CSSPropertyParserHelpers::parseRelativeRGBParametersRaw
• WebCore::Style::Builder::resolveVariableReferences
• WebCore::Style::TreeResolver::resolvePseudoElement

Suggested Fix for Shopify CDN:
Wrap relative color syntax inside @supports (color: rgb(from white r g b)) feature queries with solid RGBA fallbacks, or avoid relative color syntax on pseudo-elements in customer account web components.

No file, test, or entry point is named. Start by locating the Shadow DOM CSS for and reproduce the crash on an iOS 16 device or WebKit environment. Done means the affected styles provide compatible fallbacks or feature-query handling and the WebContent crash no longer occurs.