fix(dialog): close button will be overlayed with content, closes #1381

CHANGELOG.en-US.md

@@ -5,6 +5,7 @@
 ### Fixes
 
 - Fix `n-collapse`'s expanded status is lost when using `v-if` with `n-collapse-item`, closes [#1387](https://github.com/TuSimple/naive-ui/issues/1387).
+- Fix `n-dialog`'s close button will be overlayed with content, closes [#1381](https://github.com/TuSimple/naive-ui/issues/1381).
 
 ### Feats
 

CHANGELOG.zh-CN.md

@@ -5,6 +5,7 @@
 ### Fixes
 
 - 修复 `n-collapse` 在 `n-collapse-item` 使用 `v-if` 是展开状态丢失，关闭 [#1387](https://github.com/TuSimple/naive-ui/issues/1387)
+- 修复 `n-dialog` 的关闭按钮会被内容遮盖，关闭 [#1381](https://github.com/TuSimple/naive-ui/issues/1381)
 
 ### Feats
 

src/dialog/src/styles/index.cssr.ts

@@ -71,6 +71,7 @@ export default c([
       top: 0;
       margin: var(--close-margin);
       transition: .3s color var(--bezier);
+      z-index: 1;
     `),
     cE('content', `
       font-size: var(--font-size);