I have become really good at modifying Oslo or Seattle CSS and clients love the final product but now that I'm learning more about the Rest API and SharePoint Add-ins I wonder if it is a good approach... What I do is I choose the layout that fits my needs, then I create parts in HTML with JS and CSS then upload it to a document library and then I use the Content Editor Web Part to add it to the site, from there I start modifying the CSS and use the Rest API if needed.

I never touch any master page's file such as the CSS nor .master, my issue is, if this is ok to do it?

  • Instead of modifying master page css you can attach your css file as per your need with specific classes and ids. And If you want to modify the master page, better is to create new master page from Oslo.html or Seattle.html. You can check this url for master page creation: learningsharepoint.com/2013/03/25/… Feb 28, 2017 at 4:14
  • Guys thanks for your tips and answers! I can't up vote your answers since I have a reputation of 1 or 0, but still, thank you for taking the time!.
    Mar 2, 2017 at 3:55

2 Answers 2


It is always recommended and good approach is to create a separate css file and reference in master page to over right the default css rather than modifying the default css.

See the below forum for your reference.



It is not recommended to touch the master page in SharePoint Online! Microsoft is frequently rolling out updates that you'll miss out on when using your own master page. Instead register your alternate CSS on the Site Master Page Settings page shown below. enter image description here

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