For vh you will have to type
I always type my measures except px (native), but % and vh is always typed in front of the number.
To centre the container you can select the section and use flexbox to move your content like this:
The arrow is the flexbox setting, and the blue box is how you can centre your content.
The red marker shows the way your content is displayed (vertically or horizontally)
Let me know if you need more help