First of all Thanks for the Help in my previous post , it was indeed wprocket plugin . After I deactivated the plugin cleared all the browser cache the css are loading accurately.
I am still on my staging website , I see the content loaded before and then the overall css is applied, as it mainly happening to block css. for example my Site overwall width is 1600 and in the Block width I have set container width to 1200. when the page loads first content get shows for full width then align itself in 1200px width. I am using generatepress theme blocks.
Please note : Wp Rocket plugin is still disbaled and is this something to do with security ? as staging does not have a secure certificate.
Although it's just for 1 second it does not look good at all