Hi
You can use this custom css
.view-article .article-details .blog-details-img-wrapper .article-header{
color: #fff !important;
font-size: 80px !important;
}
Add this css code inside the custom.css file.
Note: Path towards custom CSS:
Extensions>Templates>Styles>
Click on your current default template name then choose Template Options.
Then find custom CSS within the custom code.
https://prnt.sc/pu705g
https://prnt.sc/pu70zn
In Extensions>Template> Template Options > Custom Code > Custom CSS please add this
Thanks