I have a small demo:

```
<div class="box_content_height">
    <strong>Height: </strong>
    <input type="text" name="height" id="height" value="300" />px
    <input type="submit" class="submit_advance" value="submit" />    
</div>

```

And javascript

```
$('.submit_advance').click(function() {
        var height_css = $('#height').val();
        $('ul.nav-scroll').css('max-height', height_css+'px');
});

```

When I type input = 500 is result css no change 500
How to result is 

```
.ul.nav-scroll {
    max-height: valueofinput+px
}

```