Vertical labels position

HTML

<script src="http://code.highcharts.com/highcharts.js"></script>
<div id="container" style="height: 400px"></div>

JavaScript

$(function () {
    var fontSize = 30;
    $('#container').highcharts({
         chart: {
            type: 'column'
        },
        xAxis: {
            categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
        },
        
        plotOptions: {
            series: {
                dataLabels: {
                    //align: 'center',
                    //verticalAlign:'bottom',
                    enabled: true,
                    inside:true,
                    rotation: -90,
                    //x: fontSize / 3,
                    style: {
                        fontSize: fontSize + 'px'    
                        
                    }
                }
            }
        },
        
        series: [{
            data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]        
        }]
    });
});