Bootstrap Themes in teal

NEST CoreDev


We offer an easy application of a custom Bootstrap theme in a teal app. teal uses the bslib R package which provides tools for customizing Bootstrap themes, including those of shiny apps.


teal app developers can specify custom Bootstrap themes by setting the teal.bs_theme R option, which has to be set to bslib::bs_theme object. The bslib::bs_theme(...) function creates a Bootstrap theme object, where one specifies the (major) Bootstrap version (default or one of 3, 4, or 5). Optionally one can choose a bootswatch theme and customize the app CSS with functions like bslib::bs_add_rules. Please read more about custom themes in the bslib getting started vignette. The teal.bs_theme R option has to be specified at the top of the code script.

Please install bslib package before you run the code below.

teal.bs_theme R option

options("teal.bs_theme" = bslib::bs_theme("Custom Options"))

# teal::init() app code

Bootstrap version and themes

The best and recommended ways to explore the Bootstrap themes are to use bslib::run_with_themer(shinyApp(app$ui, app$server)) or bslib::bs_theme_preview(), both of which offer an interactive explore mode (not supported for Bootstrap 3). The bslib::bs_theme_preview() is recommended when the end user does not have any shiny app yet. When you already have a shiny app and you want to test different Bootstrap themes (and CSS styling) then bslib::run_with_themer(shinyApp(app$ui, app$server)) is recommended.

Available Bootstrap versions could be checked with bslib::versions() and Bootstrap themes (bootswatch) with bslib::bootswatch_themes(version = "5").

# bslib::versions()
# bslib::bootswatch_themes(version = "5")
options("teal.bs_theme" = bslib::bs_theme(version = "5", bootswatch = "lux")
# or
options("teal.bs_theme" = bslib::bs_theme_update(bslib::bs_theme(version = "5"), bootswatch = "lux"))

Default Bootstrap theme

When using the default bslib theme for any version (3, 4 or 5), its styling might not be as expected. Please run the interactive themer (recommended) or apply a custom theme to explore all the theme options. In many scenarios updating only the theme might not be enough and e.g. font color and other specifications should be updated too.

# instead of
options("teal.bs_theme" =  bslib::bs_theme(version = "5"))
# try non-default themes
options("teal.bs_theme" = bslib::bs_theme(version = "5", bootswatch = "THEME NAME". ...))
# or run the app inside bslib::run_with_themer

Reset the Bootstrap theme

Please use the options("teal.bs_theme" = NULL) call to return to the default shiny Bootstrap for teal apps.

Theme not updated

One reason the theme is not updated could be that the web browser caches the previous one, especially when different themes are run one after another. Please, use the Cmd+Shift+R (Mac) or Ctrl+F5 (Windows) to hard refresh the webpage.

Custom teal CSS

The most important HTML tags in teal have a specific id or class, so they can be directly styled. The bslib::bs_add_rules function could be used around the bslib::bs_theme object to apply custom CSS rules.

options("teal.bs_theme" = bslib::bs_theme(version = "5") %>% bslib::bs_add_rules("Anything understood by sass::as_sass()"))

Other bslib::bs_add_* family functions could be used to specify low-level Bootstrap elements.

Bootstrap NULL vs Bootstrap 3

It is important to note that the statements options("teal.bs_theme" = NULL) and options("teal.bs_theme" = bslib::bs_theme(version = "3") are not equivalent as the bslib approximation of the default shiny theme for Bootstrap version 3 can introduce some discrepancies. One important difference is that when using bslib::bs_theme(version = "3", bootswatch = "THEME NAME") one can apply the custom Bootstrap theme. Another one is that the usage of bslib::bs_theme(version = "3") requires the installation of the latest shinyWidgets package from the main branch, see below.

# Downloading the newest shinyWidgets
# needed only when bslib::bs_theme(version = "3", ...) is used

Regular shiny::fluidPage

If you want to update the theme in a regular shiny::fluidPage-like app, you do not need the teal.bs_theme option. Simply provide the bslib::bs_theme directly: shiny::fluidPage(theme = bslib::bs_theme(...), ...).

Interactive theming guide

In this section we provide a step-by-step guide to customizing a teal application theme interactively with bslib::run_with_themer(). We recommend starting with a simple case and once you are satisfied, verifying with your full application. To that end we will use the teal application below. For this example we assume that we want to use Bootstrap 5. To start, we launch the app with bslib::run_with_themer(app$ui, app$server) instead of shiny::shinyApp.

options("teal.bs_theme" = bslib::bs_theme(version = "5"))


app <- init(
  data = teal_data(IRIS = iris), 
  filter = teal_slices(teal_slice("IRIS", "Sepal.Length", selected = c(5, 7))),
  modules = modules(example_module(), example_module()),
  header = "My first teal application"

bslib::run_with_themer(shinyApp(app$ui, app$server))

This gives us the following.

Note the Theme Customizer section on the right hand side. This was added by bslib and is how we customize our theme.

Set overall app theme

Instead of starting from scratch, we want to start with a Bootswatch theme. Let us select the Minty theme in the “Overall theme” drop-down.

bslib has updated our CSS styles to use our new theme, including the customizer theme. Additionally, if we look at our R console, we will see

####  Update your bs_theme() R code with:  #####
bs_theme_update(theme, bootswatch = "minty")

This is a helpful guide that provides code to update our theme. For teal applications we don’t actually use bs_theme_update and opt for bs_theme instead. However, the printed code will still be helpful.

Customize a bootswatch theme

Our base theme (Minty) is close to what we want but let’s make a few modifications. To start, we will increase the base font size. To do this, we choose the “Fonts” section of the customizer theme and then set a value in the “Base font size” input. We use 1.25 here, which means all our fonts will be increased by a factor of 1.25. If we check the R console, we will see bslib has printed bs_theme_update(theme, font_scale = 1.25, bootswatch = "minty"), which now includes our font size adjustment.

Finally, suppose we do not want borders to be rounded. In our customizer theme, we can go to “Options” and then uncheck the “Rounded corners” box.

As expected, our corners are no longer rounded. If we look at our R console, we will now see bs_theme_update(theme, font_scale = 1.25,enable-rounded= FALSE, bootswatch = "minty").

Apply the customized theme

Once our customization is complete, we will apply the changes to our application. To do this, we use the option teal.bs_theme like before but this time we will expand on our bslib::bs_theme call to include our changes. Luckily, the arguments that were printed to the R console when running our app in the themer can be plugged right in.

  "teal.bs_theme" = bslib::bs_theme(
    version = "5",
    font_scale = 1.25,
    `enable-rounded` = FALSE,
    bootswatch = "minty"


app <- init(
  data = teal_data(IRIS = iris),
  filter = teal_slices(teal_slice("IRIS", "Sepal.Length", selected = c(5, 7))),
  modules = modules(example_module(), example_module())

shinyApp(app$ui, app$server)

Now the application has our custom theme applied.

Please note the interactive themer only contains the most commonly applied options. For more customization options, review the bslib documentation.