将规格下架弹窗改为页面居中显示

pages/goods-update/goods-update.wxml

@@ -502,8 +502,8 @@
   </view>
   
   <!-- 规格选择弹窗 - 用于下架单个规格 -->
-  <view class="custom-select-modal" wx:if="{{showSpecUnpublishModal}}" style="position: fixed; top: 0; left: 0; right: 0; bottom: 0; background: rgba(0,0,0,0.5); display: flex; justify-content: center; z-index: 9999;" catchtouchmove="true">
-    <view style="position: fixed; bottom: 0; left: 0; right: 0; background: white; border-radius: 20rpx 20rpx 0 0; max-height: 80vh;">
+  <view class="custom-select-modal" wx:if="{{showSpecUnpublishModal}}" style="position: fixed; top: 0; left: 0; right: 0; bottom: 0; background: rgba(0,0,0,0.5); display: flex; justify-content: center; align-items: center; z-index: 9999;" catchtouchmove="true">
+    <view style="position: relative; background: white; border-radius: 20rpx; max-height: 80vh; width: 80%; max-width: 600rpx; overflow: hidden;">
       <!-- 顶部操作栏：取消和确定按钮 -->
       <view style="padding: 20rpx; display: flex; justify-content: space-between; align-items: center; border-bottom: 1rpx solid #eee;">
         <view bindtap="closeSpecUnpublishModal" style="font-size: 32rpx; color: #333; padding: 10rpx 20rpx;">取消</view>
@@ -517,7 +517,7 @@
       <!-- 规格列表 -->
       <scroll-view 
         scroll-y="true" 
-        style="max-height: 60vh; padding: 0; -webkit-overflow-scrolling: touch;"
+        style="max-height: 50vh; padding: 0; -webkit-overflow-scrolling: touch;"
         enable-back-to-top="false"
       >
         <view