#kotak-dialog {
    position:absolute;
    top:105px;
    left:80px;
    margin:0px;
    width:400px;
    height:auto;
    background-color:#fff;
    -webkit-box-shadow:0px 1px 2px rgba(0, 0, 0, 0.4);
    -moz-box-shadow:0px 1px 2px rgba(0, 0, 0, 0.4);
    box-shadow:0px 1px 2px rgba(0, 0, 0, 0.4);
    z-index:1000;
    display:none;
}
#kotak-dialog *:focus {
    outline:none;
}
#kotak-dialog h3.title {
    background-color:#3B5998;
    padding:10px 15px;
    color:#fff;
    font:normal 16px Arial, Sans-Serif;
    margin:0px 0px 0px 0px;
    position:relative;
}
#kotak-dialog h3.title a {
    position:absolute;
    top:10px;
    right:15px;
    color:#fff;
    text-decoration:none;
    cursor:pointer;
}
#kotak-dialog .isi-dialog {
    margin:15px;
    font:normal 12px Arial, Sans-Serif;
}
#kotak-dialog .button-wrapper {
    padding:10px 15px 0px;
    border-top:1px solid #ddd;
    margin-top:15px;
}
#kotak-dialog .button-wrapper button {
    background-color:#FF0C39;
    border:none;
    font:bold 12px Arial, Sans-Serif;
    color:#fff;
    padding:5px 10px;
    -webkit-border-radius:3px;
    -moz-border-radius:3px;
    border-radius:3px;
    cursor:pointer;
}
#kotak-dialog .button-wrapper button:hover {
    background-color:#aaa;
}
#dialog-overlay {
    position:fixed !important;
    position:absolute;
    z-index:999;
    top:0px;
    right:0px;
    bottom:0px;
    left:0px;
    background-color:#000;
    display:none;
}
.isi-dialog input {
    background-color:white;
    width:70%;
    margin:5px 0px 2px 15px;
    padding:2px 5px;
    border:1px solid #ccc;
    font:bold 16px Arial, Sans-Serif;
    display:block;
}

<div id="kotak-dialog">
     <h3 class="title">Login<a class="close" href="http://www.dhf.web.id#">&#215;</a></h3>

    <div class="isi-dialog">Ketik username dan sandi Anda!
        <form action="#">
            <input name="username" placeholder="Username" type="text" />
            <input name="password" placeholder="Password" type="password" />
            <div class="button-wrapper">
                <button class="okeh">Submit</button>
                <button class="close">Cancel</button>
            </div>
        </form>
    </div>
</div>
<div id="dialog-overlay"></div>
<button class="open-dialog">Login!</button>

$(function () {
    $('.open-dialog').click(function () {
        $('#kotak-dialog').show("explode", {pieces:18}, 1000);
        $('#dialog-overlay').fadeTo("normal", 0.6);
        return false;
    });
    $('#kotak-dialog .close').click(function () {
        $('#kotak-dialog').hide("explode", {pieces:27}, 1000);
        $('#dialog-overlay').fadeTo("normal", 9).hide();
        return false;
    });
    // Aksi utama dituliskan di sini, saat menekan tombol Submit
    $('#kotak-dialog .okeh').click(function () {
        alert("Tersubmit!");
    });
});

Jangan lupa juga untuk memuat library JQuery UI sebelum menerapkan kode di atas, jika tidak, kode di atas tidak akan pernah bekerja (pelajari tentang JQuery UI di sini).

• CSS
• HTML
• JQuery