Hello Yuhong and welcome to the Community!
Within Confluence Cloud there are functional differences then what would be present for Confluence Server. These types of differences include the ability to apply customization to your site which would allow you to modify the display of a theme using custom CSS. Further information on these differences may be found at Functional differences in Confluence Cloud.
I hope this proves helpful in explaining why the bullets are not currently adjustable.
@Stephen Sifers , Thanks.
I am assume somewhere in the backlog, this will be addressed, right? Is it going to addressed soon?
I really don't care what styles they actually are, you can still hard code them. I just need them to be different at different levels. Each time the indentation is changed, the bullet or number style change.
This is a great question, and the answer to this is that there is nothing currently on the roadmap to allow for customization of Confluence Cloud. There is a feature request for this which you may find at CONFCLOUD-36137. Do note that this is an older request and there are multiple reasons why customization has been disabled within Cloud products, one of the main reasons is due to security-related issues.
I hope this additional information proves helpful to you.