To edit a space's CSS style sheets:

1. 
2. Choose Stylesheet then Edit.
3. Paste your custom CSS into the text field.
4. Save your changes. The new CSS will be visible on all content pages in the space.

If your space uses the Documentation theme:

1. 
2. Click Stylesheet in the left-hand panel under the heading 'Look and Feel'.
3. Choose  Edit.
4. Paste your custom CSS into the text field.
5. Save your changes. The new CSS will be visible on all content pages in the space.