Solved Header tag H1, H2, H3 font size + CSS problem

Hallo, I need to set different header H1, H2, H3. font size for desktop, tablet and smartphone devices.
I was looking for a plugin but didn't find any plugin to do that.

I tried with custom css in Divi > Theme customizer: it works for H1, H2, H3 but the main css doesn't work anymore (the background color of the page disappears, etc.) don't understand why. So I had to delete che custom css.

This is the code I've used in Divi > Theme customizer:

@media all and (min-width: 1405px) {
h1 {
font-size: 42px!important;
}

@media all and (min-width: 1100px) and (max-width: 1405px) {
.et_pb_text_0 h1 {
font-size: 42px!important;
}

@media all and (max-width: 980px) {
.et_pb_text_0 h1 {
font-size: 36px!important;
}

and so on, for all different screen resolutions.

Thank you for your help.
Mary

 

Thank you very very much for your help: problem solved, everything works fine.