feat: allow string type z-index

src/sticky/README.md

@@ -57,7 +57,7 @@ export default {
 | Attribute | Description | Type | Default |
 |------|------|------|------|
 | offset-top | Offset top | *number* | `0` |
-| z-index | z-index when sticky | *number* | `99` |
+| z-index | z-index when sticky | *string \| number* | `99` |
 | container | Container DOM | *HTMLElement* | - |
 
 ### Events

src/sticky/README.zh-CN.md

@@ -67,7 +67,7 @@ export default {
 | 参数 | 说明 | 类型 | 默认值 |
 |------|------|------|------|
 | offset-top | 吸顶时与顶部的距离，单位`px` | *number* | `0` |
-| z-index | 吸顶时的 z-index | *number* | `99` |
+| z-index | 吸顶时的 z-index | *string \| number* | `99` |
 | container | 容器对应的 HTML 节点 | *HTMLElement* | - |
 
 ### Events

src/sticky/index.js

@@ -17,7 +17,7 @@ export default createComponent({
   ],
 
   props: {
-    zIndex: Number,
+    zIndex: [Number, String],
     container: null,
     offsetTop: {
       type: Number,