title: Initially rendering a page with a bs_theme() can be very slow for large shiny apps
body: <p>I've been trying out the <code>bslib</code> package and hit some trouble using it to style a somewhat bloated shiny app I've developed. It takes about 30 seconds before anything at all gets rendered in the browser. However if I switch to using a <code>shinythemes</code> theme instead then there is no delay.</p>
  <p>I've recreated the issue with a simple app with an inordinate number of selectize inputs. The time before rendering seems roughly proportional to the number of inputs.</p>
  <pre><code>library(shiny)
  library(bslib)
  library(shinythemes)
  
  ui &lt;- fluidPage(
    theme = bs_theme(bootswatch = &quot;slate&quot;),
    # theme = shinythemes::shinytheme(&quot;slate&quot;),
    do.call(&quot;tagList&quot;, lapply(1:200, function(x) 
      selectInput(paste0(&quot;id&quot;, x), &quot;Another input&quot;, choices = LETTERS)))
  )
  server &lt;- function(input, output, session) {}
  shinyApp(ui, server)
  </code></pre>
  <p>Anyone have any ideas what it is doing, or if there is a way around this?</p>