Unable to use textbox custom class

Hi, thanks for producing such a great theme. I’m trying to use custom CSS on a text box so that a custom font can be used. I’ve set up a child theme, and also enabled developer options so that I can chose a custom CSS class. I enter a custom class in this field, which is hp-maintext, however the Google Chrome developer tools still show that that the text box is using a <div class=”avia_textblock hp-maintext” itemprop=”text”>.

Whatever changes I make to the hp-maintext are not picked up, it only seems to be looking for (and using) avia_textblock. Is there anyway to stop avia_textblock from being used? It is the H1 heading that I would like the font changing to, and am using the following code within style.css within the child theme:

.hp-maintext .wpb_text_column h1{
font-size:21px;
font-family:MaduraiNormLight !important;
font-weight:400;
font-style:normal;
margin-top:30px;
}

Many thanks for your help