If you want the css for each section to be the same, like “FEATURED PRODUCTS” and “NEWEST ARRIVALS”. You need to add id for it. Ex: “FEATURED PRODUCTS” => #shopify-section-16311987698b44727d p{}
This is the easiest way for beginners. Alternatively, you can also add css code for each file, but it requires you to know Liquid code. Ex: https://github.com/Shopify/dawn/blob/main/sections/image-banner.liquid . https://i.imgur.com/zVkuEjB.png
Hope it helps!