chore: ts strict fixes for ui theme

.changeset/tidy-fans-clean.md

@@ -0,0 +1,5 @@
+---
+"@aws-amplify/ui": patch
+---
+
+chore: ts strict fixes for createTheme

packages/ui/src/theme/utils.ts

@@ -33,12 +33,12 @@ export function cssValue(token: BaseDesignToken): string | number {
     return referenceValue(value);
   }
 
-  if (isShadowToken(value)) {
+  if (isShadowTokenObject(value)) {
     return SHADOW_PROPERTIES.map((property) => {
       return referenceValue(
         // lookup property against `token` first for custom non-nested value, then lookup
         // property against `value` for design token value
-        isShadowToken(token) ? token[property] : value[property]
+        isShadowTokenObject(token) ? token[property] : value[property]
       );
     }).join(' ');
   }
@@ -65,7 +65,9 @@ export function isDesignToken(value: unknown): value is WebDesignToken {
   return isObject(value) && has(value, 'value');
 }
 
-export function isShadowToken(value: unknown): value is ShadowValue {
+export function isShadowTokenObject(
+  value: unknown
+): value is ShadowValue & object {
   return isObject(value) && has(value, 'offsetX');
 }