How to synchronize css code and display element with shortcode?

Hello,

I created a slider that I add to the page via a shortcode.

Since it isn’t across the entire width, I made a blue background there, which is completely done via CSS.

And this creates the problem that the CSS is processed earlier, so when the page is loaded, only the blue background is visible for a small moment, the slider is displayed with a slight delay.

Would it be possible to sync it somehow please?

Thank you

The page I need help with: [log in to see the link]