Hello!

I think there's an error in css link here:

<link rel="stylesheet" href="css:style.css" />

You see it when you check the source code. So please let me know if it is an error and if it is, then how it can be corrected.
And if it's not an error, then what is it then?

It is reserved for the file > css/custom.css
You can create an empty custom.css to solve the problem.
Here is a video, how to create a custom.css
www.joomlaplates.com/support/documentation/custom-css-in-joomla

joomlaplates wrote: It is reserved for the file > css/custom.css
You can create an empty custom.css to solve the problem.

I know about custom.css, I just don't understand the connection. Normally, external CSS files can be opened and have a valid URL. Here it's different and therefore, unusual. It's not a problem to be solved for as long as it's the way it should be. Is it?
Please explain in short if you don't mind.

The missing URL for the custom.css depends on the php code to include the css file.
If there is no css file to load, the code is blank:
>> layouts/theme.config.php

$this->addFile('css', 'css:custom.css');

Problem solved.

Okay, thanks for explanation! Though it's beyond my level of understanding (I'm not a coder), but as long it's OK and everything is fine, then I guess it's not something to worry about.