Custom Image Font (Poster Mode)

Help please? I'm in squarespace 7.0. Trying to get the headline <h3> text to go on my images in POSTER mode. It just blinks correctly and then goes back to normal again. Can anyone help me understand? You can see my CSS code in the lower left corner. Thanks!

 

Here's my code:
------

.sqs-block-image .design-layout-poster .image-title h3 {
font-family: "ag_buch";
color: #FFFFFF !important;
}

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The "ag_buch" is defined further up, and works everywhere else on the site.

Can you share link to page where you use Poster, we can check easier?

Thanks. Tuanphan.

I got my programmer friend to help me today. 

This is where we ended. In case it can help anyone:

 

.image-card-wrapper .image-title p
{
font-size: 36px !important ; 
font-size: 3.0rem !important ; 
  font-family: 'ag_buch', sans-serif !important; 

}

.image-card-wrapper .image-title p strong {

font-weight: 300 !important;  }


 

Now looking like i wanted it to.