Sharepoint 2013. CSS issue. What to twist?

Question

SharePoint

Good afternoon.
Connected css styles in seattle.master file

<SharePoint:CssRegistration Name="Themable/style.css" runat="server" />

Under admin, all the styles I use are applied. I hide blocks, adjust the font, etc.
If you log in as a user who does not have admin rights, but simply co-editing rights, then css styles are NOT applied.
Can anyone suggest how to solve the problem?
Edit core15v.css directly?