RShiny框背景色未按编码显示

Question

我正在为RShiny应用程序构建UI，但是由于某些未知的原因，fluidRow中框的背景色未显示黑色。我什至添加了一些HTML代码来强制框颜色为黑色，但仍然无法正常工作。 这是我编写的代码。想知道是否有人能找出导致此问题的原因？

fluidRow(
              box(width=12,height = 220, background = 'black',
                  sliderInput("slider_fia_prod", "Issue year:", fia_start_yr, fia_end_yr, value=c(fia_start_yr,fia_end_yr), width = '100%'),
                box(width=10, height = 90, background = 'black', 
                    div(plotlyOutput("fia_general_hor_bar"), align = "center")),
                box(width=1, height = 90, background = 'black',
                    div(checkboxGroupInput('by_mva_type', label = 'By MVA Type', choices = list('MVA' = 'A', 'Non-MVA' = 'B'), selected = c('A','B')), 
                        style = "font-size: 12px; padding: 0px", align = "left")),
                box(width=1, height = 90, background = 'black',
                    div(checkboxGroupInput('by_gmwb_rider', label = 'By GMWB Rider', choices = list('GMWB' = 'G', 'Non-GMWB' = 'N'), selected = c('N', 'G')), 
                        style = "font-size: 12px; padding: 0px", align = "left"))),
              tags$style(HTML(".box.box-solid.box-primary>.box-header {color:#fff;background:#000000}
                             .box.box-solid.box-primary{border-bottom-color:#000000;
                                                        border-left-color:#000000;
                                                        border-right-color:#000000;
                                                        border-top-color:#000000;}

                            ")))

非常感谢！