Rmarkdown font size and header

Question

I recently opened a standard Rmd file without editing anything. The default file looks like this:

Untitled.rmd

---
title: "myfile"
author: "Me"
date: "May 25, 2015"
output: html_document
fontsize: 12pt
---

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r}
summary(cars)
```

You can also embed plots, for example:

```{r, echo=FALSE}
plot(cars)
```

Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.

I wanted to create an html file corresponding to the above file so in a separate R script I did the following:

knit('Untitled.Rmd', 'doc.md')
markdownToHTML('doc.md', 'testing.html',header = TRUE)

For some reason the font size doesn't work and the header information that I was hoping for doesn't appear in my testing.html. Anyone know why this is happening?

Answer 1

This is what I used to control font size and color in an R-markdown file. It basically overrides the CSS style sheets without having to create a new file. The example changes the sizes of the headers and titles, as well as the inline text and the R-code text, and sets some colors as well.

In my case I needed to pack more information into a document that had a specified number of pages so I made everything smaller.

---
title: "This is a title"
date: 25 May 2015
output:
html_document:
theme: cerulean
---

<style type="text/css">

body{ /* Normal  */
      font-size: 12px;
  }
td {  /* Table  */
  font-size: 8px;
}
h1.title {
  font-size: 38px;
  color: DarkRed;
}
h1 { /* Header 1 */
  font-size: 28px;
  color: DarkBlue;
}
h2 { /* Header 2 */
    font-size: 22px;
  color: DarkBlue;
}
h3 { /* Header 3 */
  font-size: 18px;
  font-family: "Times New Roman", Times, serif;
  color: DarkBlue;
}
code.r{ /* Code block */
    font-size: 12px;
}
pre { /* Code block - determines code spacing between lines */
    font-size: 14px;
}
</style>


# H1 Header

Some body text

## H2 Header

More body text

### H3 Header

blah blah blah

```{r echo=T}
n <- 100
df <- data.frame(x=rnorm(n),y=rnorm(n))
```

### Another H3

Update:

Added more more styles, comments, and a bit of color to make this answer more useful. And a screen shot: