Styling H1 will not work

Hello,
I have got one page of my website and there I want to style the H1 in other size than the H1 at the other pages.
At text block element => style => font size
There is the opportunity the set the fontsize for different devices.
I have set 40px for standard device and this works for text in a <p> tag.

But now I want to set the font size for the h1 to 30px in a further text block element. And this will not work with h1.

I tried with custom css and this will not work, too.
I have set a custom css class at text block element => advanced => developer => custom css class as follows:
headline_style_home

At Enfold quick css I have the following css code:
/*Headline Style*/
.headline_style_home {
font-size: 30px !important;
}

But nothing will affect to the H1 headline with custom css class “headline_style_home” or with settings at text block element => style => font size.
Why? How to solve that?

kind regards