It is easy to add simple customization for a page / block by inserting CSS and JS code in a few fields added in the page/block options.
Your Custom CSS can be applied on each breakpoint set in Weltpixel -> Frontend options -> Breakpoints. You can set your desired breakpoints for different screen sizes resolutions starting from low resolution dedicated for mobile, tablet and up to large screens.
You can add your own Custom CSS and JS for any static page. Your Custom CSS for static pages can be inserted in Content -> Pages -> [edit desired page] -> Design.
You can add your own Custom CSS and JS for any static block you wish.
Your Custom CSS for static blocks can be inserted in Content -> Blocks -> [edit desired block] and right below the magento editor you can find the fields for the custom CSS and JS.