As already mentioned, make sure there is no white space (spaces, tabs, new lines etc.) before the opening <?php tag in your controller. If you have a closing ?> tag, then this can be removed, as it can often cause issues with redirect.
In this case, if you aren't concerned about having the function's name in the URL (this will not change the URL to show the function that you are calling (logotyp()) in the URL, whereas the redirect function would)/refreshing the page, then you could just call the relevant function directly in your index() function:
public function index()
{
$this->logotyp();
}
For your second issue (CSS not loading); it is probably occuring because the link to its path is incorrect. Using the base_url function from CodeIgniter's URL Helper you can easily generate the correct path. I don't know where your CSS file(s) is located, but for this example I'll assume that, relative to the site root, it is here: assets/css/style.css. Simply add the path relative to web root as so:
<link href="<?php echo base_url("assets/css/style.css"); ?>" type="text/css" rel="stylesheet">
link_tag() in the HTML Helpercan also help with the generation of stylesheet links.
