Add background noise effect to section backgrounds

Hi all, novice here wondering if someone can help.

I'm wondering if there's a way to apply an animated noise/grain effect to section backgrounds without the background needing to be a photo. An example of what I'm trying to achieve is on this website.

I've tried adding PNGs of a noise texture to each section, but because my sections are all different sizes, the grain effect differs in size/intensity from section to section. It's also not animated if I do it this way.

I also found this website which feels like it could be useful, I just don't know which bit of code I need to insert into my Squarespace site, and where.

Hope someone can help!

This is available in the background image settings as an image effect.

After you've added the image background, click on Image Effects, and then select Film Grain.

Thanks Ziggy, and apologies if I haven't explained myself properly, but I don't want to have to add an image to every background section. Is there a way of applying the same effect to all section backgrounds without the use of a background image?

I was actually wondering the same thing! I think #page, #page .page-section, #page .page-section .section-background might work, but I just want to use a textured and transparent .png file to overlay all my color backgrounds for all sections of the page.