How To Change Blog Container Margin/Padding?

In Wordpress Admin Panel go to Appearance > Editor section

Open Editor

After opening Editor Section, click Toggle Navigation which in on left top corner of Editor Section Screen.

Open Toggle Navigation

Now Click on Templates and Open Archive

Open Archive

After Archive is opened, select List Views.

Select List View

In List Views, open the heirarchy of group Select Column. Make sure that your Main Blog column is selected in Block Editor.

Select Column

Now select Block Settings in Right Top Corner, under Dimensions change Padding and Margin. If either of Padding or Margin is missing from the Dimensions panel, click on the three dots to enable it.

Changing Margin Padding

Once you change the padding or margin, you should see the effect right away in the Block Editor.