### Install shinythemes package

Source: https://rstudio.github.io/shinythemes

Install the shinythemes package from CRAN. Requires Shiny 0.11 or later.

```r
install.packages("shinythemes")
```

--------------------------------

### Add themeSelector() to UI for live theme switching

Source: https://rstudio.github.io/shinythemes

Add shinythemes::themeSelector() to the UI to get a select box for choosing themes without reloading. Intended for development only; replace with a fixed theme argument once chosen.

```r
shinyApp(
  ui = fluidPage(
    shinythemes::themeSelector(),  # <--- Add this somewhere in the UI
    sidebarPanel(
      textInput("txt", "Text input:", "text here"),
      sliderInput("slider", "Slider input:", 1, 100, 30),
      actionButton("action", "Button"),
      actionButton("action2", "Button2", class = "btn-primary")
    ),
    mainPanel(
      tabsetPanel(
        tabPanel("Tab 1"),
        tabPanel("Tab 2")
      )
    )
  ),
  server = function(input, output) {}
)
```

--------------------------------

### Directory structure for custom theme in www/

Source: https://rstudio.github.io/shinythemes

Place a custom CSS file (e.g., mytheme.css) in the www/ subdirectory of the app. Files there are automatically served to the app.

```text
myapp
 |-- server.R
 |-- ui.R
 |-- www/
      |-- mytheme.css
```

--------------------------------

### Reference custom theme in ui.R

Source: https://rstudio.github.io/shinythemes

In ui.R, set the theme argument to the filename of the custom CSS file (e.g., "mytheme.css"). The file must be in the www/ directory.

```r
fluidPage(
  theme = "mytheme.css",
  ...
)
```

--------------------------------

### Use shinytheme() in single-file app.R

Source: https://rstudio.github.io/shinythemes

For a single-file app, pass shinytheme("united") to the theme argument of fluidPage inside shinyApp(). The server function is defined inline.

```r
## app.R ##
library(shinythemes)

shinyApp(
  ui = fluidPage(theme = shinytheme("united"),
    ...
  ),
  server = function(input, output) { }
)
```

--------------------------------

### Use shinytheme() in ui.R with fluidPage

Source: https://rstudio.github.io/shinythemes

In ui.R, pass shinytheme("cerulean") to the theme argument of fluidPage. The library(shinythemes) call is required.

```r
## ui.R ##
library(shinythemes)

fluidPage(theme = shinytheme("cerulean"),
  ...
)
```

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