统一聊天页的头像大小，改用rpx2px的计算，84rpx

pages/im/private/chat.vue

@@ -7,7 +7,7 @@
                 <view class="cell" v-for="(item, index) in messages" :key="index">
                     <view class="time">{{ item.sentTime|timeCustomCN }}</view>
                     <view :class="['cell-item', item.messageDirection == 1 ? 'right' : 'left']">
-                        <u-avatar class="avatar" size="40" shape="square"
+                        <u-avatar class="avatar" :size="avatarSize" shape="square"
                             @click="showUser(item.senderUserId, item.messageDirection)"
                             :src="contact(item.senderUserId).portraitUrl" />
                         <view class="msg">
@@ -37,7 +37,9 @@
     import showImage from '../components/showImage'
     import showText from '../components/showText'
     import showCall from '../components/showCall'
-    import sentMessageBar from '../components/sentMessageBar'
+    import sentMessageBar from '../components/sentMessageBar'
+    import utils from '@/utils/index.js'
+    
     export default {
         components: {
             sentMessageBar,
@@ -47,7 +49,8 @@
             showCall
         },
         data() {
-            return {
+            return {
+                avatarRpx: 84,
                 targetId: '',
                 messages: [],
                 conversationType: 1,
@@ -58,7 +61,10 @@
                 }
             }
         },
-        computed: {
+        computed: {
+            avatarSize() {
+                return utils.rpx2px(this.avatarRpx)
+            },
             latestMessage() {
                 if (this.messages.length) {
                     return this.messages[0]
@@ -179,7 +185,8 @@
                     .time {
                         text-align: center;
                         font-size: 24rpx;
-                        color: #666;
+                        color: #666;
+                        margin-bottom: 10rpx;
                     }
 
                     .cell-item {