How to reduce the gap between form label value or any fields

Summary:

I'm creating an application having form with input parameters but the gap between the fields is too much. How can I reduce it ?

Also, How to know what classes we need to use for various fields like to center, align, as shown below. I don't know how we select those classes names (I'm new to VBCS and did not find any doc for same). Please help

Content (required):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):