问如何使这个Ul元素位于Div元素下面？

EN

<div id="dashboard">
    <div id="Sidebar">
        <div id="User-Icon"></div>
        <ul>
            <li a href="#">Home</li>
            <li a href="#">Home</li>
            <li a href="#">Home</li>
            <li a href="#">Home</li>
            <li a href="#">Home</li>
        </ul>
    </div>

    <div id="Dashboard">
    </div>

    <div id="UserFeed">
    </div>
</div>

  * {
        Font-Family: Arial;
        Margin: 0;
        Padding: 0;
    }
    
    #dashboard {
        display: flex;
        height: 100vh;
        width: 100vw;
    }
    
    #Sidebar {
        background-color: #5c5c5c;
        height: 100%;
        width: 20%;
        display: flex;
        justify-content: center;
        align-self: flex-end;
    }   
    
    #Dashboard {
        background-color: #999999;
        height: 100%;
        width: 50%;
    }
    
    #UserFeed {
        background-color: #D9D5D6;
        height: 100%;
        width: 30%;
    }
    
    #User-Icon {
        width: 150px;
        height: 150px;
        background-color: white;
        border-radius: 50px;
        margin-top: 50px;
    }
    
    ul {
        
    }
    
    
    li {
        list-style: none;
        margin-top: 50px;
    }