完善描述和tabbar背景色

pages/API/theme-change/theme-change.uvue

@@ -11,7 +11,7 @@
 
     <view>
       <view class="uni-title uni-common-mt">
-        <text class="uni-title-text"> 修改appTheme主题 </text>
+        <text class="uni-title-text"> 修改appTheme主题（此处仅为演示API，本应用并未完整适配暗黑模式） </text>
       </view>
     </view>
     <view class="uni-list uni-common-pl">

pages/tabBar/API.uvue

 <template>
   <!-- #ifdef APP -->
-  <scroll-view style="flex: 1" enable-back-to-top="true">
+  <scroll-view style="flex: 1;background-color: #f8f8f8;" enable-back-to-top="true">
   <!-- #endif -->
     <view class="uni-container">
       <view class="uni-header-logo">

pages/tabBar/CSS.uvue

 <template>
   <!-- #ifdef APP -->
-  <scroll-view style="flex: 1" enable-back-to-top="true">
+  <scroll-view style="flex: 1;background-color: #f8f8f8;" enable-back-to-top="true">
   <!-- #endif -->
     <view class="uni-container">
       <view class="uni-header-logo">

pages/tabBar/template.uvue

 <template>
   <!-- #ifdef APP -->
-  <scroll-view style="flex: 1" enable-back-to-top="true">
+  <scroll-view style="flex: 1;background-color: #f8f8f8;" enable-back-to-top="true">
   <!-- #endif -->
     <view class="uni-container">
       <view class="uni-header-logo">