help does not let me add lines of HTML or css in appearance

nights, does anyone know why I get this error and somehow why it doesn't let me add elements or html code?

EduKenzay the appearance tab only allows css/Stylesheets not HTML.

In general, I tried it with a css test and it didn't leave me the same error either.

EduKenzay Can you show us the CSS code you tried? And can you translate the text in the red box for us?