Where are you getting the .blog-cover class selector from? As far as I can tell by looking at the demo site for the Attila theme, .blog-cover isn’t used anywhere in the HTML, so that would be why targeting that selector is not creating any changes on your site.
Note that different themes will use different classes, IDs etc. (the names of classes and IDs aren’t formally standardized and are simply chosen by whoever develops the theme) so you need to ensure that you find and target the correct selector when trying to modify CSS properties.
As an aside, you will occasionally find that you may need to use or find it useful to use !important when trying to override existing CSS e.g. width: 50% !important; however that would certainly not be the case here.
This will rather just be a case of finding and targeting the correct selector.
In the second screenshot you’ve attached
You can see in the top right style.css:1 - that’s telling you that this CSS is coming from your custom style sheet (and of course the 1 indicates that .blog-cover is on line 1). So by that, I mean, it’s not an indication that .blog-cover actually exists in the HTML of the Attila theme or its CSS.
To be honest though, I’m not entirely sure why it’s showing width: 100%; if you’ve set it to width: 50%; in your code injection… that’s a bit of an anomaly to me. I’m not an expert though.
Anyway, if you tell or show me which part of the Attila theme you are trying to change, I can help you find the correct selector and code to accomplish that goal.
I think the missing component in this issue is the tutorial itself. I’m not sure why it was taken down.
The large /assets/css/style.css file you’re seeing is what Gulp spat out. Files that end in .scss are most likely the source files for Gulp. These are the files you should edit. Casper has development instructions on how to work locally and edit the theme code: