I’m writing an online book (bs4_book) with the bookdown package in RMarkdown. Inside the markdown there are Python chunks with simple operations like importing libraries and arithmetic calculations. I’ve been looking for a way to make the lines inside the Python chunks numbered by changing parameters inside the style.css file. Although I succeeded, this method also numbers the output of the cells, and I personally don’t like it.
I know there must be a way to define it inside the .css file, but I don’t know the language.

Here’s my style.css file:

p.caption {
  color: #777;
  margin-top: 10px;
}
p code {
  white-space: inherit;
}
pre {
  word-break: normal;
  word-wrap: normal;
}
pre code {
  white-space: inherit;
}
pre.sourceCode {
    counter-reset: line;
    line-height: 0.8; 
}
pre.sourceCode > code > span:before {
    content: counter(line);
    display: inline-block;
    border-right: 1px solid #ddd;
    padding-right: 0.5em;
    margin-right: 0.5em;
    color: #888;
}

I´ve tried this with no succed:

pre.sourceCode > code > span {
    display: block;
    counter-increment: line;
}
pre.output, pre.verbatim {
  counter-reset: none !important;
  padding-left: 0 !important;
  list-style-type: none !important;
  border: none !important;
}
pre.output > code > span:before, pre.verbatim > code > span:before {
  content: none !important;
}