优化主题切换器和用户通知组件样式，添加文件大小显示，调整布局和样式变量

src/@layouts/components/VerticalNavLayout.vue

@@ -101,6 +101,13 @@ export default defineComponent({
 @use '@layouts/styles/placeholders';
 @use '@layouts/styles/mixins';
 
+.layout-page-content {
+  position: relative;
+  z-index: 1;
+  margin-block-start: 0;
+  padding-block-start: 0;
+}
+
 .layout-wrapper.layout-nav-type-vertical {
   // TODO(v2): Check why we need height in vertical nav & min-height in horizontal nav
   block-size: 100%;
@@ -208,11 +215,4 @@ export default defineComponent({
     padding-inline-start: 0;
   }
 }
-
-.layout-page-content {
-  position: relative;
-  z-index: 1;
-  margin-block-start: calc(variables.$layout-vertical-nav-navbar-height - 42px);
-  padding-block-start: 0;
-}
 </style>