Change the fontsize of a title. Has as?

I have this:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Operacional.Views.Indicadores"
             xmlns:local="clr-namespace:Operacional.ViewModels"
             xmlns:badge="clr-namespace:Operacional"
             Title="[email protected]"             
             Icon="person.png"
             >

How can I change fontsize? By Resource > ToolBar I get it, but I had difficulty changing it in runtime