style(admin): 优化子菜单样式

- 显示子菜单图标并增加缩进
- 调整子菜单项的样式，包括图标和文本的间距

Author: qnnp-me

src/plugin/admin/public/component/pear/css/module/menu.css

@@ -265,3 +265,19 @@
 	display: inline-block;
 	vertical-align: middle;
 }
+
+/* 显示子菜单图标并增加缩进 */
+.pear-nav-tree .layui-nav-child dd a i {
+	display: inline;
+	margin-left: 12px;
+	margin-right: 6px;
+}
+.pear-nav-tree .layui-nav-child dd a i[class=''] {
+	margin-right: 0;
+}
+.pear-nav-tree .layui-nav-child dd dl {
+	margin-left: 12px;
+}
+.pear-nav-tree .layui-nav-child dd a span {
+	margin-left: 0 !important;
+}