How to change wordpress post editor add title font size?

Question

I'm using Astra theme and the add and edit new post or page title font size is really big. I tried editing using css in custom css but maybe editor styesheel not the same like frontend style so it didn't work. Is there any way I can edit this or can only edit within theme file directly?

Here is the css code that I can change in inspect mode but dont know where to change in the actual theme file:

.edit-post-visual-editor h1.block-editor-block-list__block {
    font-size: 2rem;
    font-family: 'Montserrat', sans-serif;
    /*default font size: 70px*/
}