Find the right CSS selector

Hello,
I am building a simple website with Site Origins Page Builder Plugin. I really like the plugin but there is one issue I cannot fix. There is too much white space between the widgets in one row. I want to achieve that the padding/margin between all widgets in any row is the same. In Settings > Page Builder I set the value for margin-bottom Row/Widget to 10 px, but it only seems to effect the Rows. I tried different selectors and styles like padding: 0 and margin: 0 to see if there is any effect, but I couldn’t find the one I need.

Please help me to find the appropiate selector that I need to change the margin-bottom / padding-bottom of all widgets and explain me in a few sentences how you found it. For me it’s often tricky to find the selector I need even if I use the browser function to observe elements.

Thank you for your help.

Kind Regards,
Michael