How can I give padding at the sidebard

Hi, how can I set the same padding at the sidebar area?
The site can be visited here.

In addition, these days I often ask CSS questions. I know how to use "inspect" at the Chrome browser to look at CSS of the section of a webpage, but I cannot specify which part I should modify. For example, in the below, I do not know which part I should change. I know that I can freely try and change in the inspect of Chrome, but I cannot correctly bring it to Simple CSS edit of Wordpress. Could you give me tips on how to do it or guide me a good online course or videos which teach this aspect?