js
import '../../index.css'

....菜单代码

        <Menu
          theme="dark"
          mode="inline"
          style={{ width: 250 }} 要同步
          defaultSelectedKeys={[activePath]}
          selectedKeys={[activePath]}
        >

css
.ant-layout-sider-dark {
    flex: 0 0 250px !important;
    max-width: 250px !important;
    min-width: 250px !important;
    width: 250px !important;

}