Icons are missing from the Admin area

If you would see a screen like this:

It means, that the fonts aren't correctly set up in your server. Open up your .htaccess file, and put these codes into it:

AddType font/ttf .ttf
AddType font/eot .eot
AddType font/otf .otf
AddType font/woff .woff
AddType font/woff2 .woff2
<FilesMatch "\.(ttf|otf|eot|woff|woff2)$">
    <IfModule mod_headers.c>
        Header set Access-Control-Allow-Origin "*"
    </IfModule>
</FilesMatch>

or into your web.config file this code:

<staticContent>
<clientCache cacheControlCustom="public" cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />
<remove fileExtension=".woff" />
<remove fileExtension=".woff2" />
<mimeMap fileExtension=".woff" mimeType="application/x-font-woff" />
<mimeMap fileExtension=".woff2" mimeType="application/font-woff2" />
</staticContent>

which usually solves it, but if you are not sure about yourself, or this doesn't have an effect, you should contact your server host, and ask them for help, tell them, that your fonts aren't loading correctly.

WP Engine server

If you're running PHP 7.4 or above, contact your host for assintance, as they no longer support htaccess file.

Own server

Windows Server

If you are managing your own Windows server, you could try to follow the "Fix static file serving" part here.

Akeeba Admin Tools Joomla

In Joomla Akeeba Admin Tools could block files too. If you have installed it in your website, add this line to its  Allow direct access, except .php files, to these directories setting:

media/smartslider3/src/SmartSlider3/Application/Admin/Assets/