Divs in HTML and CSS

This is content,for more check
<!--
#wrapper {
    width: 700px;
    height: 1000px;
    margin-left: auto;
    margin-right: auto;
    border-style: solid;
    border-width: thin;
    
}

#header {
    width: 600px;
    height: 100px;
    margin-left: auto;
    margin-right: auto;
    border-style: solid;
    border-width: thin; 
    background-color: #CCC;
    
    
}
#menu {
    width: 100px;
    height: 600px;
    margin-left: 50px;
    border-style: solid;
    border-width: thin; 
    float: left;
    
    
}
#content {
    width: 475px;
    height: 600px;
    margin-right: 50px;
    border-style: solid;
    border-width: thin; 
    float: right;
    
    
}

<!DOCTYPE html>
<HTML lang="en-US">
    <HEAD>
        <TITLE> Divs in HTML and CSS </TITLE>
        <META charset="utf-8" />
        <META name="keywords" content="" />
        <META name="description" content="" />
        <link rel="stylesheet" href="Stylesheet.css" type="text/css" />
    </HEAD>
    <BODY>
        

        <div id="wrapper">
        

        <div id="header"></div>

        <div id="menu">This is the menu</div>

        <div id="content">This is content</div>
        </div>
    </BODY>
</HTML>



-->