R Autofit DT table width and height in xaringan HTML5 presentation

Update based on your update

You're missing the closing > on styles. However, it still used it, which I find interesting. Well, used it and then ignored all but padding.

The title caused the underlying structure to change. This will work for the styles.

<style>
div.remark-slide-content {
  padding: 1em; /*default is 1em 4em*/
}
.dataTables_wrapper {
  font-size: .5em;
}
</style>

I noticed a few other things. I'm really surprised you didn't get an error for the "Data Table" chunk name. Chunk names shouldn't have whitespace. Just because it isn't causing a problem now doesn't mean it won't down the road. You also had out chunk options. They are ignored; you can remove them.

You also have "---" after the chunk xaringan-themer and before # Data Table. This is giving you a blank slide. (You may have done this on purpose and wanted it there; I just thought I would mention it.)

Altogether:

---
title: "Ed Edd n Eddy"
subtitle: ""
author: "Ed"
institute: "Gravy"
date: "`r format(Sys.Date(),'%e de %B, %Y')`"
output:
  xaringan::moon_reader:
    css: xaringan-themer.css
    lib_dir: libs
    nature:
      highlightStyle: github
      highlightLines: true
      countIncrementalSlides: false
editor_options: 
  chunk_output_type: console
---

<style>
div.remark-slide-content {
  padding: 1em; /*default is 1em 4em*/
}
.dataTables_wrapper {
  font-size: .5em;
}
</style>

```{r setup, include=FALSE}
options(htmltools.dir.version = FALSE)
library(knitr)
library(tidyverse)
library(sf)
library(plotly)
library(leaflet)
library(leaflet.extras)
library(DT)
library(simplevis)
library(sfheaders)
library(xaringanthemer)

```

```{r xaringan-themer, include=FALSE, warning=FALSE}

style_mono_accent(
  base_color = "#3399FF",
  header_font_google = google_font("Josefin Sans"),
  text_font_google   = google_font("Montserrat", "300", "300i"),
  code_font_google   = google_font("Fira Mono"),
 # background_image = "/BCLogo540.jpg"
  #background_position
)
# ?style_mono_accent
```


# Data Table

<!--- I removed whitespace from this chunk name! --->
<!--- I also removed  out.width= "400px", out.height="600px" from chunk options these out settings were ignored--->

```{r DataTable,echo=FALSE, message=FALSE, warning=FALSE}

# First import the shapefile
#sf= st_read("path/sf.shp", quiet = TRUE)
# Convert to df (This is the sample data you have in the question)
df <- structure(list(
  City = c("HOLLYWOOD", "PLANTATION", "Davie", "HOLLYWOOD", "PLANTATION"), 
  Zipcode = c("33024", "33317", "33314", "33024", "33317"), 
  Date = structure(c(18996, 18633, 19011, 19012, 19016), 
                   class = "Date"), 
  Year = c(2022, 2021, 2022, 2022, 2022), 
  Month = c(1, 1, 1, 1, 1), Day = c(4, 6, 19, 20, 24), 
  SR = c("SR-22-001", "SR-22-002", "SR-22-003", "SR-22-004", "SR-22-006"), 
  Permit = c("06-SE-2433290", "06-SE-2444371", "06-SM-2448351", "06-SM-2448625", NA),
  `Owner/Agent` = c("Pardo, G A & Elaine Nu-Black Septic Co", 
                    "Alshine Mondesir A Tip Top Septic", 
                    "Charlotte Ingmire Mr. C's Pumbling & Septic Inc.", 
                    "SRP Sub LLC Statewide Septic Cont Inc", 
                    "John Nelson Mr. C's Pumbling & Septic Inc."), 
  Address = c("1111 Harding St Hollywood, FL 33024", 
              "5555 W Broward Blvd Plantation, 33317", 
              "1111 SW 74 Ave Davie, 33314", 
              "2222 Thomas Street Hollywood, FL 33024", 
              "333 Bryan Blvd Plantation, 33317")), 
  sfc_columns = c("x", "y"), class = "data.frame", row.names = c(NA, -5L))

# Table
datatable(df,
          extensions = 'FixedColumns',
  options = list(
    dom = 't'))  %>%
  formatStyle(names(df),
              background = 'lightblue', angle = -90,
              backgroundSize = '98% 88%',
              backgroundRepeat = 'no-repeat',
              backgroundPosition = 'center')

```

Original answer

Once you added a slide title, it changed the CSS assigned to the class remark-slide-content. However, it looks like it maintained the padding settings.

Alright, I'm not sure what your preferred table is. (I'm guessing preferred may have gone out the window in lieu of something like @##$^$ FIT $#$^#^... I've had many of these moments. So I picked a table above at random.

You needed styles. So you were on the right track. The div that I've used has the style display: table-cell, so it was rather ideal for manipulation.

This is all you need.

<style>
div.remark-slide-content {
  padding: 1em; /*default is 1em 4em*/
  font-size: .7em;
  vertical-align: middle; /*if you don't want it in the middle, delete this*/
}
</style>

Altogether, now:

---
title: "Ed Edd n Eddy"
subtitle: ""
author: "Ed"
institute: "Gravy"
date: "`r format(Sys.Date(),'%e de %B, %Y')`"
output:
  xaringan::moon_reader:
    css: xaringan-themer.css
    lib_dir: libs
    nature:
      highlightStyle: github
      highlightLines: true
      countIncrementalSlides: false
editor_options: 
  chunk_output_type: console
---

<style>
div.remark-slide-content {
  padding: 1em; /*default is 1em 4em*/
  font-size: .7em;
  vertical-align: middle; /*if you don't want it in the middle, delete this*/
}
</style>

```{r doasyouretold,echo=F,include=F}

library(tidyverse)
library(DT)

df <- structure(list(
  City = c("HOLLYWOOD", "PLANTATION", "Davie", "HOLLYWOOD", "PLANTATION"), Zipcode = c("33024", "33317", "33314", "33024", "33317"), 
  Date = structure(c(18996, 18633, 19011, 19012, 19016), class = "Date"), 
  Year = c(2022, 2021, 2022, 2022, 2022), Month = c(1, 1, 1, 1, 1), Day = c(4, 6, 19, 20, 24), 
  SR = c("SR-22-001", "SR-22-002", "SR-22-003", "SR-22-004", "SR-22-006"), 
  Permit = c("06-SE-2433290", "06-SE-2444371", "06-SM-2448351", "06-SM-2448625", NA),
  `Owner/Agent` = c("Pardo, G A & Elaine Nu-Black Septic Co", "Alshine Mondesir A Tip Top Septic", 
                    "Charlotte Ingmire Mr. C's Pumbling & Septic Inc.", "SRP Sub LLC Statewide Septic Cont Inc", 
                    "John Nelson Mr. C's Pumbling & Septic Inc."), 
  Address = c("1111 Harding St Hollywood, FL 33024", "5555 W Broward Blvd Plantation, 33317", 
              "1111 SW 74 Ave Davie, 33314", "2222 Thomas Street Hollywood, FL 33024", 
              "333 Bryan Blvd Plantation, 33317")), 
  sfc_columns = c("x", "y"), class = "data.frame", row.names = c(NA, -5L))

```


```{r gimmeNow,echo=F}

datatable(df,
         # style = "font-size: 75%; width: 75%")  %>% <- this doesn't go here...
         ) %>% 
  formatStyle(names(df), background = 'lightblue', angle = -90,
              backgroundSize = '98% 88%', backgroundRepeat = 'no-repeat',
              backgroundPosition = 'center')

```