When you add two or more Content Editor Web Part your page, sometimes this error occurs;
Error Definition;
line: 2135
Char: 4
Error: ‘style.display’ is null or not an object
code: 0
Error Type;
This is a Content Editor Web Part Javascript Error;
Error Resolution;
“When you delete or close your web parts, you wont get any error;” if the sentence is true for you then,
your problem is copying / pasting CEWP information. Probably, you prepared your text on Office Word then you copied it to the CEWP. Seems like the error appears, because of conflicting IDs.
So try these;
——-——-——-——-——-——-
Before you try, please copy ‘Rich Text Editor‘ and ‘Source Editor‘ text to a safety place. Just a precaution 
——-——-——-——-——-——-
- Open ‘Modify Web part Page‘,
- Select ‘Rich Text Editor‘,
- Copy the text,
- Select ‘Source Editor‘,
- Paste the text,
- Then Open again ‘Rich Text Editor‘ and stylize your text all over again
