Columns are not getting displayed in tablet mode as per wireframes

Hi Experts, I am going through the Rapid Developer training course. In Chapter 3.4.1 “Add columns to your App”, I was trying to add 4 columns in a page using the layout grid. Based on documentation and wireframes, in tablet mode, 2 rows with 2 columns should be displayed but in all devices, I am seeing 1 row with 4 columns. Please let me know how to display 2*2 in tablet mode. Additional Information I am using Mendix Studio Pro 8.8.0 Attaching the screenshot of Mainframes based on the chapter content.Training Link Page      
1 answers

In the steps this is performed by setting the correct css class on the columns, see step 9

The class col-sm-6 needs to be applied to all columns, this will display the columns correctly in the tablet design mode.