Hide logo and page number only for scrolling slides in RMarkdown

Question

I produce a deck of ioslides with logo and page number in RStudio with rmarkdown. If the content is to big for a slide I can add slides > slide { overflow: scroll; }to my .css file and supress the logo and page number with slides > slide:not(.nobackground):after {content: '';} and slides > slide:not(.nobackground):before {background: none;}.

But I want to keep the logo and page numbers to every page with no overflow. So I tried to reference the css-styles to the #id of the overfull page but that doesn't work.

EDIT: Here is what I tried.

My .Rmd file:

---
title: "Untitled"
author: "Samuel Merk"
output: 
  ioslides_presentation:
    css: mycss.css
    logo: logo.png
date: "12 Juli 2016"
---



## Very long slide

This is the long slide.

efewg  
sdfg  
sdfg  
sdfg  

sdfg  
sdfg  
sdfg  

  efewg  
sdfg  
sdfg  
sdfg  

sdfg  
sdfg  
sdfg  


## Bullets

- Bullet 1
- Bullet 2
- Bullet 3

My Customization of the .css file

#very-long-slide {
  slides > slide { overflow: scroll; }
  slides > slide:not(.nobackground):after {content: '';}
  slides > slide:not(.nobackground):before {background: none;}
 }