types(Stepper): improve theme prop typing (#8489)

src/stepper/Stepper.tsx

@@ -30,11 +30,13 @@ function add(num1: number, num2: number) {
   return Math.round((num1 + num2) * cardinal) / cardinal;
 }
 
+export type StepperTheme = 'default' | 'round';
+
 export default defineComponent({
   name,
 
   props: {
-    theme: String,
+    theme: String as PropType<StepperTheme>,
     integer: Boolean,
     disabled: Boolean,
     allowEmpty: Boolean,

src/stepper/index.ts

@@ -1,7 +1,8 @@
 import { withInstall } from '../utils';
-import _Stepper from './Stepper';
+import _Stepper, { StepperTheme } from './Stepper';
 
 const Stepper = withInstall<typeof _Stepper>(_Stepper);
 
 export default Stepper;
 export { Stepper };
+export type { StepperTheme };