🐛[BUG] 通过token修改样式 展开的子菜单背景色不生效

### 🐛 bug 描述

展开的菜单背景色是白色，没有按照预期设定的token颜色

### 📷 复现步骤

https://pro-components.antdigital.dev/~demos/packages-layout-src-components-layout-tab-api-demo-theme

### 🏞 期望结果

背景色是设定的颜色

### 💻 复现代码

https://pro-components.antdigital.dev/~demos/packages-layout-src-components-layout-tab-api-demo-theme

### © 版本信息

- ProComponents 版本: 官方示例网站
- umi 版本
- 浏览器环境
- 开发环境 [e.g. mac OS]

### 🚑 其他信息


Start with the linked theme demo and reproduce the expanded submenu background-color issue using the configured design token. Trace the Layout or tab-menu styling from that demo to identify where the submenu background is determined. Done means the expanded submenu uses the configured token color rather than white.

Written by the indexing model from the issue text.