[Doc] optimzie demo display (#626)

docs/demos/views/cell-swipe.vue

@@ -1,7 +1,7 @@
 <template>
   <div>
-    <van-notice-bar>{{ $t('tips') }}</van-notice-bar>
     <demo-section>
+      <van-notice-bar>{{ $t('tips') }}</van-notice-bar>
       <demo-block :title="$t('basicUsage')">
         <van-cell-swipe :right-width="65" :left-width="65">
           <span slot="left">{{ $t('button1') }}</span>

docs/demos/views/checkbox.vue

@@ -65,8 +65,6 @@ export default {
 
 <style lang="postcss">
 .demo-checkbox {
-  background: #fff;
-
   .van-checkbox {
     margin: 10px 0 0 20px;
   }

docs/demos/views/pull-refresh.vue

@@ -1,11 +1,11 @@
 <template>
-  <van-pull-refresh v-model="isLoading" @refresh="onRefresh">
-    <demo-section name="pull-refresh" background="#fff">
+  <demo-section name="pull-refresh">
+    <van-pull-refresh v-model="isLoading" @refresh="onRefresh">
       <demo-block :title="$t('basicUsage')">
         <p>{{ $t('text') }}: {{ count }}</p>
       </demo-block>
-    </demo-section>
-  </van-pull-refresh>
+    </van-pull-refresh>
+  </demo-section>
 </template>
 
 <script>
@@ -42,6 +42,13 @@ export default {
 
 <style lang="postcss">
 .demo-pull-refresh {
+  .van-pull-refresh {
+    &,
+    &__track {
+      height: 100%;
+    }
+  }
+
   p {
     margin: 10px 0 0 15px;
   }

docs/demos/views/radio.vue

@@ -66,8 +66,6 @@ export default {
 
 <style lang="postcss">
 .demo-radio {
-  background: #fff;
-
   .van-radios {
     padding: 0 20px;