Remove borders around ggplot2 in quarto revealjs presentation

Question

I am trying to make a quarto presentation using revealjs. When the ggplot renders (page 2; see below for a reproducible example) there is a black border around the rendered plot. How can one remove this border?

Quarto revealjs presentation code:

---
title: "Test Presentation"
format: 
  revealjs:
    theme: [default, custom.scss]
---

## Some plot

```{r}
library(ggplot2)

ggplot(mtcars) +
  geom_boxplot(aes(as.factor(cyl), disp, fill = cyl)) +
  theme_minimal() +
  theme(
      legend.position = "none",
      panel.grid = element_blank(),
      axis.title = element_text(size = 20, color = "#fefefe"),
      axis.text = element_text(size = 15, color = "#fefefe"),
      plot.title = element_text(size = 20, color = "#fefefe"),
      plot.background = element_rect(fill = "#505050"),
      panel.background = element_rect(fill = "#505050"),
      axis.line.x.top = element_line(color = "#fefefe"),
      axis.line.x.bottom = element_line(color = "#fefefe"),
      axis.line.y.left = element_line(color = "#fefefe"),
      axis.line.y.right = element_line(color = "#fefefe")
    ) +
    guides(x.sec = "axis", y.sec = "axis")
```

custom.scss code:

/*-- scss:defaults --*/

// fonts
$font-family-sans-serif: "Palatino Linotype", "Book Antiqua", Palatino,
  FreeSerif, serif !default;

// colors
$body-bg: #505050;
$body-color: #ffffff;
$link-color: #51483d !default;
$selection-bg: #26351c !default;

// headings
$presentation-heading-font: "Palatino Linotype", "Book Antiqua", Palatino,
  FreeSerif, serif !default;
$presentation-heading-color: #ffffff !default;

/*-- scss:rules --*/

.reveal a {
  line-height: 1.3em;
}

Answer 1

To remove the border around your plot set e.g. color = NA or size=NA in theme option plot.background:

---
title: "Test Presentation"
format: 
  revealjs:
    theme: [default, custom.scss]
---

## Some plot

```{r}
library(ggplot2)

ggplot(mtcars) +
  geom_boxplot(aes(as.factor(cyl), disp, fill = cyl)) +
  theme_minimal() +
  theme(
      legend.position = "none",
      panel.grid = element_blank(),
      axis.title = element_text(size = 20, color = "#fefefe"),
      axis.text = element_text(size = 15, color = "#fefefe"),
      plot.title = element_text(size = 20, color = "#fefefe"),
      plot.background = element_rect(fill = "#505050", color = NA),
      panel.background = element_rect(fill = "#505050"),
      axis.line.x.top = element_line(color = "#fefefe"),
      axis.line.x.bottom = element_line(color = "#fefefe"),
      axis.line.y.left = element_line(color = "#fefefe"),
      axis.line.y.right = element_line(color = "#fefefe")
    ) +
    guides(x.sec = "axis", y.sec = "axis")
```