How to change Chart series tips style (font and font-size)

Below is what I tried (style, bodyStyle, font)

Here is a series

Code:

{type: 'column', xField: 'datereleve',yField: "nbdeces", axis: 'left', 
        tips: 
        {
            trackMouse: true,
            width: 150,
            height: 50,
            renderer: function(storeItem, item) {
                this.setTitle(titre + '<br/>' + storeItem.get('datereleve') + '<br/>n=' + storeItem.get('nbdeces'));
            },
            bodyStyle: {
                font: '5px Helvetica, sans-serif'
            }
            //style:{'font-size':'4px'}
            //font:"5px Helvetica, sans-serif"
        }
    }

thanks!