This PR update stylesheet for code blocks with line-numbers.
Examples are at the bottom.

Changes

Background of <div class="sourceCode"> is changed to transpreant.

In some syntax highlighting, background color of <div class="sourceCode"> are specified (e.g., tango)
This cause ugly appearance especially in theme: darkly
As long as line numbers are not used, background color of the div tags are not visible.
Thus, I considered it is okay to letting them transparent.

Background of pre for chunk output are changed to white

Previously, specifying class.output="numberLines" caused output code block to have gray background where white is expected.
This is fixed by exact matching of class attributes.
Thus, white background are only applied when

• pre has no class (just like before)
• pre has the classes only related to line numbering on code blocks.

The latter is approached by the exact matching of classes.
Exact matching is required for the backward compatibility.
Otherwise, Bootstrap would not work to fill background colors for example by class.output = "numberLines bg-warning".

Note

If the output pre tag has the lineAnchors class, but not the numberLines, it is filled with gray.
Because line numbering is not working.

Examples

Before

After

Source

---
output: 
  html_document:
    highlight: tango
    theme: darkly
---

## Code blocks with line numbers

`class.source='numberLines'` and `class.output='numberLines'`

```{r, class.source='numberLines', class.output='numberLines'}
"hello"
```

`class.output='numberLines lineAnchors'`

```{r, class.source='numberLines', class.output='numberLines lineAnchors', echo = FALSE}
"hello"
```

`class.output='lineAnchors numberLines'`

```{r, class.source='numberLines', class.output='lineAnchors numberLines', echo = FALSE}
"hello"
```

`class.output='lineAnchors'`

```{r, class.source='numberLines', class.output='lineAnchors', echo = FALSE}
"hello"
```

## Bootstrap friendly

`class.output='numberLines bg-warning'` properly applies Bootstrap's `bg-warning` class to style background.

```{r class.output='numberLines bg-warning', echo = FALSE}
"hello"
```