Hi,
did you check this documents:
- https://success.outsystems.com/Documentation/SILK_UI_Framework/04_Understanding_the_Screen_Layout#Silk_UI_Web
- https://success.outsystems.com/Documentation/SILK_UI_Framework/06_Customizing_Silk_UI
- https://www.outsystems.com/learn/lesson/1276/creating-a-custom-layout
- https://success.outsystems.com/Documentation/11/Developing_an_Application/Design_UI/Look_and_Feel/Design_the_Layout_of_Screens_Using_Placeholders
- https://success.outsystems.com/Documentation/11/Developing_an_Application/Design_UI/Patterns/Using_Traditional_Web_Patterns/Layout
Cheers