refactor(nav-bar): move customStyle to root view (#3371)

fix #3369

packages/nav-bar/README.md

@@ -60,7 +60,7 @@ Page({
 | placeholder | 固定在顶部时是否开启占位 | _boolean_ | `false` | - |
 | border | 是否显示下边框 | _boolean_ | `true` | - |
 | z-index | 元素 z-index | _number_ | `1` | - |
-| custom-style | 自定义样式 | _string_ | - | - |
+| custom-style | 根节点自定义样式 | _string_ | - | - |
 | safe-area-inset-top | 是否留出顶部安全距离（状态栏高度） | _boolean_ | `true` | - |
 
 ### Slot

packages/nav-bar/index.wxml

@@ -4,9 +4,9 @@
 
 <view
   class="{{ utils.bem('nav-bar', { fixed }) }} custom-class {{ border ? 'van-hairline--bottom' : '' }}"
-  style="{{ baseStyle }}"
+  style="{{ baseStyle }}; {{ customStyle }}"
 >
-  <view class="van-nav-bar__content" style="{{ customStyle }}">
+  <view class="van-nav-bar__content">
     <view class="van-nav-bar__left" bind:tap="onClickLeft">
       <block wx:if="{{ leftArrow || leftText }}">
         <van-icon