Can not change font size of heading

Hey, I ve tried to change the font size of headings like <h1> and <h2>. I tried to change it in stlye.ccs for each heading but it did not work. Neither did the following code snippet in CSS Customer work: #site-title { font-size: 3rem; } My website: www.wasseraktien.net Could someone help me here? Regards, Ben