Hi @juanajaafar,
You can add a class pam
to your shortcode,
e.g.
[content_band bg_color="#434343" style="color: #ffffff; text-align: justify;" border="all" inner_container="true" class="pam"]
This will give padding to your content band on all sides. You can learn more about this Spacing Helpers Classes here.
My advice for you though since you’re now using Gutenberg (for posts) and Cornerstone (for pages), please stop using that content band shortcode and utilize the native features.
For example that white text color on gray background-color, you can easily do that with Gutenberg text block.

Much more with Cornerstone.
Block Editor Handbook (Gutenberg)
Cornerstone Elements
Hope it helps,
Cheers!