Fix review UI (#27322)

Close #26730


1. The `diff-detail-box` was abused, it shouldn't be used for
"DiffFileList/DiffFileTree".
2. Fix the sticky position for various screens.



![image](558a5c06-c94c-4e5c-8395-d38473dd21c2)


![image](3390fb0e-7dc7-457f-bd0c-398fdb6d24c0)


![image](d19dd350-aecf-4909-8ef9-73b09d94560e)

web_src/js/components/DiffFileList.vue

@@ -36,7 +36,7 @@ export default {
 };
 </script>
 <template>
-  <ol class="diff-detail-box diff-stats gt-m-0" ref="root" v-if="store.fileListIsVisible">
+  <ol class="diff-stats gt-m-0" ref="root" v-if="store.fileListIsVisible">
     <li v-for="file in store.files" :key="file.NameHash">
       <div class="gt-font-semibold gt-df gt-ac pull-right">
         <span v-if="file.IsBin" class="gt-ml-1 gt-mr-3">{{ store.binaryFileMessage }}</span>

web_src/js/components/DiffFileTree.vue

@@ -126,7 +126,7 @@ export default {
 };
 </script>
 <template>
-  <div v-if="store.fileTreeIsVisible" class="gt-mr-3 gt-mt-3 diff-detail-box">
+  <div v-if="store.fileTreeIsVisible" class="gt-mr-3">
     <!-- only render the tree if we're visible. in many cases this is something that doesn't change very often -->
     <DiffFileTreeItem v-for="item in fileTree" :key="item.name" :item="item"/>
     <div v-if="store.isIncomplete" class="gt-pt-2">