title: Background in shiny absolutePanel
body: <p>I want to set the background of <code>absolutePanel</code> as transparent, but all controls in the panel as normal.</p>
  
  <p>A css style is added through tags$style, but all child controls become as transparent. How should I achieve this?</p>
  
  <p>PS: My css codes below don't work</p>
  
  <pre><code>library(shiny)
  ui &lt;- shinyUI(
  
      fluidPage(
          tags$head(tags$style(
          HTML('
               #input_date_control {opacity : 0;}
               #sel_date {opacity: 1;}')
      )),
          absolutePanel(
          sliderInput('sel_date', NULL, 0, 5, 5, width = '80%')
          , id = "input_date_control", class = "panel panel-default", fixed = TRUE
          , draggable = FALSE, top = 'auto', left = '20', right = 'auto', bottom = 20
          , width = '60%', height = 'auto'
      )))
  
  server &lt;- function(input, output, session) {
  
  }
  
  shinyApp(ui, server)
  </code></pre>