I'm sorry what do you mean by css spaghetti? What exactly do you want to put in main.css? 

I mean a cell of code which I cannot change in custom css. Example:
I have display: none for slideshow. Problem: when I write display: block and check in page inspector - I realize that it is not overwritten. But the question is NOT how to overwrite it in a correct way. The question IS: why it is not in main.css and NOT in custom css field? I use responsive theme. Why should we load 5 KB of extra code on phone? We have to optimize speed.

Yes some pages still have page and inline css in them.  Eventually it may be all moved to the main css.  But this is a long process and the mix of needed features and other script necessities has to have a place in the road map as well.  It is a work in progress. 

Several plugins contain their own css for styling which is not part of the base css. When you encounter these you will need to use !important.
(i.e. display: none !important;)
This will override the plugin's css.

Quote from Darryl B Several plugins contain their own css for styling which is not part of the base css. When you encounter these you will need to use !important.
(i.e. display: none !important;)
This will override the plugin's css.

Cool! Thanks! As I understand, to remove that pieces I need to find the code in the core files and plugin files and remove/replace them manually. The main idea is to optimixe the code, so I have to create my own theme instead of that, which I use now with custom css in order to minimize css code on the page.

If you remove them from the file they will not show on anything; even desktop. You will want to address mobile screens with media queries.  Media queries allow you to style elements to adapt to different screen sizes, or to not show them at all on different screen sizes. You can add media queries in the custom css as well.

Thanks! I remember about @media =) Thanks

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