The images for the ckeditor need to be uploaded to your custom style, until that is done it will look this way and that's why in the default style it works fine i.e. the images are already present in /images but your custom style has a folder within /images/stylesfoldername/ that you need to upload the correct images to

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Locate sprite.png in the normal styles /editor/ folder, then upload sprite.png to the custom styles /editor/ folder to fix.