cart 样式bug，

1.数字显示在总计前面
2.总计样式bug

pages/cart/cart.wxml

@@ -66,8 +66,8 @@
 
 
 <view class="billing-btn">
-  <view wx:if="{{coupon}}">
-    <view class="total">总计：¥{{amount}}元 {{'-' + coupon['coupon-value'] + '元优惠券' }}</view>
+  <view wx:if="{{coupon}}" class="total">
+    <view>总计：¥{{amount}}元 {{'-' + coupon['coupon-value'] + '元优惠券' }}</view>
   </view>
   <view wx:else class="total">
     <view>总计：¥{{amount}}元</view>

pages/cart/cart.wxss

@@ -92,6 +92,7 @@
 }
 
 .quantity .number {
+  z-index: 1;
   border-top: 1rpx solid lightgrey;
   border-bottom: 1rpx solid lightgrey;
   line-height: 50rpx;
@@ -109,6 +110,7 @@
 }
 
 .billing-btn {
+  z-index:2;
   position: fixed;
   bottom: 0;
   width: 100%;