Default headings are shown here:
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Heading_Elements#examples
I am surprised the H5 and H6 fonts are so small.
Your CSS for <h1> to <h6> is in this file:
https://www.fotov60.com/wp-content/litespeed/css/5dcb158dce52540584d3bae115f63f3c.css?ver=bf25a
As the code has been minified, you can unminify it using https://unminify.com/ (or a similar website). You will then see that the CSS for <h1> to <h6> starts at line 171.
Instead of editing that code, you could append CSS to it which will overrule previous declarations of the same properties.
You can use the shorthand font property:
. . . and the CSS color property:
As far as I can see your webpage is not downloading the Orkney font.
Now you know why I would never use WordPress 
.