How to customize the Headings in the post that they are automatically bold?

Is there a way to customize the headings in the posts in a way that they are automatically bold? I’ve tried to customize the CSS in the editor.php like that:

h2 {
font-size: 27px;
font-weight: bold;
line-height: 38px;
margin-top: 30px;
margin-bottom: 20px;
}

but there is no change, when I look at the posting. Can you please help me?

Thank you very much!
Greetings
Kathrin

I found the option in the themepanel 🙂

Greetings Kathrin