I've noticed that my main site uses styles/corev4.css while the subsites use various revisions of _layouts/1040/styles/Themable/corev4.css.

I have to modify both. While I can access styles/corev4.css, how to get to _layouts/1040/styles/Themable/corev4.css?

1 Answer 1


It is strongly advised against modifying the corev4.css file.

This main reasons being that as soon as you apply the next update, your css customisations will be lost as the file will be overwritten, and your changes affect the entire farm.

It's recommended that you create a new CSS file, store it either in a folder in LAYOUTS in the SharePointRoot folder on the server, or in the Style Library in your site collection - and reference this CSS from the AlternateCSS property for the site (through either managed Code or PowerShell), or modify your masterpage to use this new CSS alongside Corev4.

  • 2
    The next update being a sharepoint SP (Service Pack) or CU (Cumulative Update), not the update of your own feature.
    – Bart
    Jun 6, 2011 at 13:48
  • thanks, but i think this only partially solves the problem. i'm fin with modifying the master pages, but again, i should modify the main site's masterpage and all the masterpages that have been cloned while creating each new subsite!
    – pistacchio
    Jun 6, 2011 at 14:06
  • I'm not going to create another answer, but James is spot on here. NEVER modify the out of the box style sheets, JS, or masterpages. If you need to make changes, make copies, modify the copies, and deploy via a solution. If you've deployed your custom master/css via a solution a single upgrade command will push any changes to all instances of those files (since they're ghostable), you don't have to touch every one out there.
    – webdes03
    Jun 6, 2011 at 19:18

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