A lot of trial and error with custom CSS:
.game_frame
{
background:none;
}
.html_embed_widget button.button.load_iframe_btn {
display: inline-flex;
align-items: center;
justify-content: center;
gap: 10px;
width: 300px;
height: 50px;
font-size: 0;
}
.html_embed_widget button.button.load_iframe_btn > .svgicon {
flex: 0 0 auto;
margin: 0;
}
.html_embed_widget button.button.load_iframe_btn::after {
content: "Get clicking";
font-family: "Cracker Winter", sans-serif;
font-size: 24px;
line-height: 1;
}