The <
at the start and the >
at the end cause the problem when echoing in your custom_login_css
function. Replace them with < >.
The <
and >
are HTML entities meaning that if you want to print to your page a HTML reserved character you have to use this entities so the browser will understand that you don’t want to use the HTML characters as code but to display it.
More about HTML entities : https://en.wikipedia.org/wiki/HTML_entity