In the Visual Properties panel, the Content Width slider and Horizontal Padding are linked in the Alignment and Spacing section. Moving the slider from the left side changes the left padding value, and moving the slider from right changes the right padding value. The exact change is replicated in the Content Width slider when you change the left or right Horizontal padding values.
If you want to add padding at the top or bottom of the selected content block, enter the desired values for the Top and Bottom padding by changing the values in Vertical padding.
Select the Autofit height checkbox to adjust the height of the SVG content block to fit the slide.