Modal Dialog in Shiny: Can adjust width but not height

In my Shiny app, I have several modal windows from the shinyBS package. I am able to adjust the width of these modal windows like so:

tags$head(tags$style(HTML('

                                                  .modal-lg {
                                                  width: 1200px;
                                                  }
                                                  #abs_1 {background-color: white;;}
                                                  #clear{background-color: turquoise3;;}
                                                  #disease{background-color: turquoise3;;}
                                                  #bleach{background-color: turquoise3;;}
                                                  #regionSelect{background-color: turquoise3;;}
                                                  #yearSelect{background-color: turquoise3;;}
                                                  #speciesSelect{background-color: turquoise3;;}
                                                  ')))

And altering the number of pixels in the width argument changes the width of the modal windows. However, if I use height instead of width, altering the number of pixels has no effect on the height of the modal windows. Why might this be?