The border-width property can take either one of three keywords or a length value. : border width : Box Model HTML CSS TUTORIALS

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The border-width property can take either one of three keywords or a length value.


 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
                      "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns='http://www.w3.org/1999/xhtml' xml:lang='en'>
    <head>
        <title>border</title>
        <style rel='stylesheet' type='text/css'>
div#border-width {
    overflow: hidden;
}
div#border-width div {
    float: left;
    border-style: solid;
    border-color: red;
    margin: 0 5px;
}
div#thin {
    border-width: thin;
}
div#medium {
    border-width: medium;
}
div#thick {
    border-width: thick;
}
        
        </style>
    </head>
    <body>
        <div id='border-width'>
            <div id='thin'>thin</div>
            <div id='medium'>medium</div>
            <div id='thick'>thick</div>
        </div>
    </body>
</html>