Edit in JSFiddle

<div data-role="page" id="login">
    
    <div data-role="header">
        <h1>Acme Corporation</h1>
    </div>
    
    <div data-role="content">
        <form id="frmLogin" class="validate">
            <div data-role="fieldcontain">
                <label for="email">Email: </label>
                <input type="text" id="email" name="email" class="required email" />
            </div>
            
            <div data-role="fieldcontain">
                <label for="password">Password: </label>
                <input type="password" id="password" name="password" class="required" />
            </div>
            
            <div class="ui-body ui-body-b">
                <fieldset class="ui-grid-a">
                    <div class="ui-block-a"><a id="btnCancel" href="#" data-role="button" data-theme="d" data-icon="delete">Cancel</a></div>
                    <div class="ui-block-b"><button id="btnLogin" type="submit" data-theme="a" data-icon="check">Log In</button></div>
                </fieldset>
            </div>
        </form>
        
    </div>
    
</div>

// if placeholder is supported
if (Modernizr.input.placeholder) {
    $("input").each(function(index, element) {
        var placeholder = $("label[for=" + element.id + "]").hide().text();
        $(element).addClass("ui-input-text-placeholder")
            .attr("placeholder", placeholder);
    });
}

input.ui-input-text-placeholder, textarea.ui-input-text-placeholder {
    width: 98% !important;
}