@OsmandFernando
The best way to do this is to define what size the font should be in a variable. I always put code like this in the OnStart property of my app:
Set(StyleSettings,{
Color: Black,
Font: Open Sans,
FontSize: 16
})
Then for any label or text input I input the Size as a variable
StyleSettings.FontSize
When a change is needed I just alter it in the OnStart property and click Run App OnStart to refresh the App.
Set(StyleSettings,{
Color: Black,
Font: Open Sans,
FontSize: 10
})
Here's what you can do if none of your style settings are stored in a variable yet.
You can select all of the DataCardValues & Keys on a form using this method (credit to @AlanChai ).
1. Select the form
2. Change from vertical to horizontal
3. Click the undo button
4. Done

You can also select all of the Cards by doing this:
1. Ctrl+Click on DataCard1
2. Ctrl+Click on DataCard2
3. Ctrl+Click on DataCard3
4. Press Ctrl+A
5. Done

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