"sketchy" theme: checkboxes look off with bootstrap 5

[MadhulikaTanuboddi]

1. Run the following RMD

---
title: "Flexdashboard theming demo"
runtime: shiny
output: 
  flexdashboard::flex_dashboard:
    orientation: rows
    theme: 
      version: 5
    social: menu
    source_code: embed
    navbar:
      - { title: "About", href: "https://google.com", align: right, icon: glyphicon-time}
      - { title: "Home", href: "https://google.com", align: right, icon: fa-facebook }
---

```{r, include=FALSE}
library(flexdashboard)
library(ggplot2)
bslib::bs_themer()
thematic::thematic_rmd(font = "pacifico",bg = "black")

TAB1 =====================================

Column {data-width=650 .tabset}

Chart A

checkboxInput("checkbox", label = "Choice A", value = TRUE)

checkboxGroupInput("checkGroup",
          label = "Checkbox group",
          choices = list("Choice 1" = 1, "Choice 2" = 2,
                         "Choice 3" = 3),
          selected = 1)

2. Select "sketchy" theme
3. Notice the checkboxes (in the dashboard and also in the interactive themer)

<img width="1177" alt="sketchy_theme_checkboxes_bootstrap_5" src="https://user-images.githubusercontent.com/5369655/138189994-bffaee92-9829-4761-bfa7-bf3082b727eb.png">

[cpsievert]

A more minimal example:

browsable(fluidPage(
  theme = bslib::bs_theme(
    version = 5,
    bootswatch = "sketchy"
  ), 
  checkboxGroupInput("foo", "Sketchy", c("a", "b", "c"), selected = "a")
))

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