title: Ant design fixed side menu issue
body: <p>I tried to added one page content to fixed left side menu and scroll content, i tried to use <code>position:fixed</code> style. but not working correctly,   anyone know how to do that correctly, <a href="https://stackblitz.com/edit/react-ktlku4" rel="nofollow noreferrer">stack blitz here</a></p>
  
  <p>my code here</p>
  
  <pre><code>import React, { Component } from 'react';
  import { render } from 'react-dom';
  import 'antd/dist/antd.css';
  
  import { Layout, Menu, Breadcrumb, Icon } from 'antd';
  
  const { SubMenu } = Menu;
  const { Header, Content, Footer, Sider } = Layout;
  import './style.css';
  
  class App extends Component {
    constructor() {
      super();
      this.state = {
        name: 'React'
      };
    }
  
    render() {
      return (
          &lt;Layout&gt;
      &lt;Header className="header"&gt;
        &lt;div className="logo" /&gt;
        &lt;Menu
          theme="dark"
          mode="horizontal"
          defaultSelectedKeys={['2']}
          style={{ lineHeight: '64px' }}
        &gt;
          &lt;Menu.Item key="1"&gt;nav 1&lt;/Menu.Item&gt;
          &lt;Menu.Item key="2"&gt;nav 2&lt;/Menu.Item&gt;
          &lt;Menu.Item key="3"&gt;nav 3&lt;/Menu.Item&gt;
        &lt;/Menu&gt;
      &lt;/Header&gt;
      &lt;Content style={{ padding: '0 50px' }}&gt;
        &lt;Breadcrumb style={{ margin: '16px 0' }}&gt;
          &lt;Breadcrumb.Item&gt;Home&lt;/Breadcrumb.Item&gt;
          &lt;Breadcrumb.Item&gt;List&lt;/Breadcrumb.Item&gt;
          &lt;Breadcrumb.Item&gt;App&lt;/Breadcrumb.Item&gt;
        &lt;/Breadcrumb&gt;
        &lt;Layout style={{ padding: '24px 0', background: '#fff' }}&gt;
          &lt;Sider width={200} style={{ background: '#fff' }}&gt;
            &lt;Menu
              mode="inline"
              defaultSelectedKeys={['1']}
              defaultOpenKeys={['sub1']}
              style={{ height: '100%' }}
            &gt;
              &lt;SubMenu
                key="sub1"
                title={
                  &lt;span&gt;
                    &lt;Icon type="user" /&gt;
                    subnav 1
                  &lt;/span&gt;
                }
              &gt;
                &lt;Menu.Item key="1"&gt;option1&lt;/Menu.Item&gt;
                &lt;Menu.Item key="2"&gt;option2&lt;/Menu.Item&gt;
                &lt;Menu.Item key="3"&gt;option3&lt;/Menu.Item&gt;
                &lt;Menu.Item key="4"&gt;option4&lt;/Menu.Item&gt;
              &lt;/SubMenu&gt;
              &lt;SubMenu
                key="sub2"
                title={
                  &lt;span&gt;
                    &lt;Icon type="laptop" /&gt;
                    subnav 2
                  &lt;/span&gt;
                }
              &gt;
                &lt;Menu.Item key="5"&gt;option5&lt;/Menu.Item&gt;
                &lt;Menu.Item key="6"&gt;option6&lt;/Menu.Item&gt;
                &lt;Menu.Item key="7"&gt;option7&lt;/Menu.Item&gt;
                &lt;Menu.Item key="8"&gt;option8&lt;/Menu.Item&gt;
              &lt;/SubMenu&gt;
              &lt;SubMenu
                key="sub3"
                title={
                  &lt;span&gt;
                    &lt;Icon type="notification" /&gt;
                    subnav 3
                  &lt;/span&gt;
                }
              &gt;
                &lt;Menu.Item key="9"&gt;option9&lt;/Menu.Item&gt;
                &lt;Menu.Item key="10"&gt;option10&lt;/Menu.Item&gt;
                &lt;Menu.Item key="11"&gt;option11&lt;/Menu.Item&gt;
                &lt;Menu.Item key="12"&gt;option12&lt;/Menu.Item&gt;
              &lt;/SubMenu&gt;
            &lt;/Menu&gt;
          &lt;/Sider&gt;
          &lt;Content style={{ padding: '0 24px', minHeight: 280,textAlign: "center" }}&gt;    ...
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  &lt;/Content&gt;
        &lt;/Layout&gt;
      &lt;/Content&gt;
      &lt;Footer style={{ textAlign: 'center' }}&gt;Ant Design ©2018 Created by Ant UED&lt;/Footer&gt;
    &lt;/Layout&gt;
      );
    }
  }
  
  render(&lt;App /&gt;, document.getElementById('root'));
  </code></pre>