Open a modal pop in HTML5 is very simple with the help of CSS3.
HTML Part

<a href="#Modal">Modal Popup</a>
<div id="Modal" class="modalDialogBox">
    <div>
        <a href="#close" title="Close" class="closeButton">X</a>
        <h2>Modal Popup window</h2>
        <table style="width: 100%">
            <tr>
                <td>Description - CSS3 make it simple to open a modal popup.</td>
            </tr>
        </table>
    </div>
</div>

CSS Part

<style>
.modalDialogBox{
            position: fixed;
            font-family: Arial, Helvetica, sans-serif;
            top: 0;
            right: 0;
            bottom: 0;
            left: 0;
            background: rgba(0,0,0,0.8);
            z-index: 99999;
            opacity: 0;
            -webkit-transition: opacity 400ms ease-in;
            -moz-transition: opacity 400ms ease-in;
            transition: opacity 400ms ease-in;
            pointer-events: none;
        }

        .modalDialogBox:target {
            opacity: 1;
            pointer-events: auto;
        }

        .modalDialogBox > div {
            width: 600px;
            position: relative;
            margin: 20% auto;
            padding: 5px 20px 13px 20px;
            border-radius: 10px;
            background: #fff;
            background: -moz-linear-gradient(#fff, #999);
            background: -webkit-linear-gradient(#fff, #999);
            background: -o-linear-gradient(#fff, #999);
        }

        .closeButton{
            background: #606061;
            color: #FFFFFF;
            line-height: 25px;
            position: absolute;
            right: -12px;
            text-align: center;
            top: -10px;
            width: 24px;
            text-decoration: none;
            font-weight: bold;
            -webkit-border-radius: 12px;
            -moz-border-radius: 12px;
            border-radius: 12px;
            -moz-box-shadow: 1px 1px 3px #000;
            -webkit-box-shadow: 1px 1px 3px #000;
            box-shadow: 1px 1px 3px #000;
        }
        .closeButton:hover {
            background: #00d9ff;
        }
    </style>