Background in CSS: the problem that the url (image) cannot be displayed

Just encountered a strange problem, such a piece of CSS code:

Background: url (images/bg/bg1.gif) no-repeat;

This Code does not show any background image, but collapsed...
The code is certainly okay. Even if I haven't located the background image, I will not consider it for the moment, because I don't have this problem here... As a result, I searched Google and found many people with this problem... But there is not much information that really points out the problem...

What are the real problems?

The background file and background image are stored in the images directory of the same level as the style directory. Therefore, the CSS here should be written as follows:

Background: url (../images/bg/bg1.gif) no-repeat;