I want to add some CSS in my site. I read on others questions that it's better to override CSS. I'm OK with that (Tutorial here).
But, I browsed every folder of my site in SharePoint Designer and I have not seen a .css file, not even the corev4.css.
So my question is : where can I create and override a CSS file for the AllItems.aspx page ? I want to modify all the entire page, like the ribbon and the menu to make a new site.
From this documentation by MS, I cannot find the _styles folder.
NB: I specify that I'm not the Central Administrator and this is SharePoint 2010.