feat: support custom dropdownStyle (#437)

* feat: support custom  dropdownStyle

* feat: support custom  dropdownStyle

---------

Co-authored-by: kiner-tang(文辉) <[email protected]>

Author: kiner-tang

src/Cascader.tsx

@@ -194,6 +194,7 @@ const Cascader = React.forwardRef<CascaderRef, InternalCascaderProps>((props, re
     popupClassName,
     dropdownClassName,
     dropdownMenuColumnStyle,
+    dropdownStyle: customDropdownStyle,
 
     popupPlacement,
     placement,
@@ -427,7 +428,10 @@ const Cascader = React.forwardRef<CascaderRef, InternalCascaderProps>((props, re
         prefixCls={prefixCls}
         autoClearSearchValue={autoClearSearchValue}
         dropdownMatchSelectWidth={dropdownMatchSelectWidth}
-        dropdownStyle={dropdownStyle}
+        dropdownStyle={{
+          ...dropdownStyle,
+          ...customDropdownStyle,
+        }}
         // Value
         displayValues={displayValues}
         onDisplayValuesChange={onDisplayValuesChange}

tests/index.spec.tsx

@@ -1033,6 +1033,11 @@ describe('Cascader.Basic', () => {
     mount(<Cascader value={'bamboo' as any} />);
   });
 
+  it('support custom cascader', () => {
+    const wrapper = mount(<Cascader dropdownStyle={{ zIndex: 999 }} open />);
+    expect(wrapper.find('.rc-cascader-dropdown').props().style.zIndex).toBe(999);
+  });
+
   it('`null` is a value in Cascader options should throw a warning', () => {
     const errorSpy = jest.spyOn(console, 'error').mockImplementation(() => null);
     mount(