In Sharepoint Online portal I have a scripts folder inside the style library. These scripts are used on some pages through the script editor webpart with script tag. The user, which I used to upload these scripts, can see them in style library and on pages. But the new user created by administration center on portal.office.com can't see files in style library and script files keep showing not found error (404) in browser console. How must I grant permissions for the new users?
Try change the permission level of those users and add Manage Lists list permission.
Typically the Style Resources Reader group has restricted read to the root style library. This group contains all authenticated users by default. First check to see if this group exists on the library and does have the all authenticated users in it.
Second, check to make sure all of your assets are checked in as major versions and approved if necessary.
If all of these are correct, you could alter the Style Resources Readers group to have read permission on the library.