How to add background for H2 , H3 tags

Hi Friends,
I would like to have the same style of h2 and h3 tags only in the posts.
https://prnt.sc/lmq7j3

Please see above example, i am not a coder so please explain clearly.
I checked an this example from anoter blog, and it seems they have below codes somewhere; i am not sure how to do the same. Please advise.

.td-post-content h2 {

font-size: 19px;
color: white;
background-color: #8c8c8c;
border-radius: 15px;
padding: 15px;

Hi Catalin,

I currently have newsmag Travel Demo installed, no other updates.

The screenshot i provided is from another blog, can i share that blog’s URL here or via email?

Let me know,
Thanks.

Hi Catalin,

Bogdan already answered to this question via email, please disregard my question.
Regards.