Hi Mauricio,
If you open the developer tools in Chrome, or any other dev tool in other browser, in the Elements tab, you can see that every time a tooltip is generated, a div appears in the body container of the dashboard.
That div has the CSS class "tipsy", and there is other children divs accordingly.
So to change the layout of the tooltip you need to create a external css file with the properties that you want to apply to it.
Best regards