fix spin demo css

components/spin/demo/delayAndDebounce.md

@@ -10,7 +10,7 @@ Specifies a delay for loading state. If `spinning` ends during delay, loading st
 
 ```html
 <style>
-  .content{
+  .spin-content{
     border: 1px solid #91d5ff;
     background-color: #e6f7ff;
     padding: 30px;
@@ -19,7 +19,7 @@ Specifies a delay for loading state. If `spinning` ends during delay, loading st
 <template>
   <div>
     <a-spin :spinning="spinning" :delay="delayTime">
-      <div class="content">
+      <div class="spin-content">
         可以点击‘切换’按钮，延迟显示 loading 效果。当 spinning 状态在 `delay` 时间内结束，则不显示 loading 状态。
       </div>
     </a-spin>

components/spin/demo/nested.md

@@ -10,7 +10,7 @@ Embedding content into `Spin` will alter it into loading state.
 
 ```html
 <style>
-  .content{
+  .spin-content{
     border: 1px solid #91d5ff;
     background-color: #e6f7ff;
     padding: 30px;
@@ -19,7 +19,7 @@ Embedding content into `Spin` will alter it into loading state.
 <template>
   <div>
     <a-spin :spinning="spinning">
-      <div class="content">
+      <div class="spin-content">
         可以点击‘切换’按钮，控制本区域的spin展示。
       </div>
     </a-spin>

components/spin/demo/tip.md

@@ -10,7 +10,7 @@ Customized description content.
 
 ```html
 <style>
-  .content{
+  .spin-content{
     border: 1px solid #91d5ff;
     background-color: #e6f7ff;
     padding: 30px;
@@ -19,7 +19,7 @@ Customized description content.
 <template>
   <div>
     <a-spin tip="Loading...">
-      <div class="content">
+      <div class="spin-content">
         我的描述文案是自定义的。。。
       </div>
     </a-spin>