Edit in JSFiddle

$(document).ready(function(){
   
    // Immerse yourself in squares.
    var dim = Math.round(($('#boxen').parent().width() - 16) / 8) * 8;
    $('#boxen').width(dim);
    $('#boxen').height(dim);
    var box_count = Math.pow(dim / 8, 2);
    
    // We'll do it live!
    for (var i=0; i<box_count; i++){

        var r = Math.round(Math.random() * 255);
        var g = Math.round(Math.random() * 255);
        var b = Math.round(Math.random() * 255);
        var color = 'rgb(' + r + ', ' + g + ', ' + b + ')';
        $('<li>').attr('style', 'background-color: ' + color).appendTo('#boxen');

    }
                    
});
<ul id="boxen"></ul>
#boxen{
    background-color: #ccc;
}
#boxen li{
    display: block;
    width: 8px;
    height: 8px;
    float: left;
}