Wordpress mods to css so i can add sliders

Esssentially we have a developer who has developed a site based on the avada theme.

Now he tells me that its impossible to have a slider on any other page/post as he can't do it without affecting the styling of the site.

So I need someone to have a quick look at the css and mod it or set up another page template, but do not affect the site style.

I need to add sliders to pages/posts asap.