如何取消闪亮警报并输入颜色

我有一个闪亮的应用程序，用户可以选择下载数据。弹出一个提示，提示他们输入用户名。如果他们的用户名与列表匹配，则可以下载数据。如何将inputPlaceholder = "enter_username"文本的颜色更改为较深的颜色？此外，如何将闪亮警报中取消按钮的颜色更改为红色？在用户界面中，我尝试使用CSS指定颜色，但没有成功。我检查了网页，试图确定正确的命名。

在哪里可以找到有关使用CSS指定用户界面调整的更多信息？

服务器

library(shiny)
library(shinyalert)

data <- data.frame(x=rnorm(10),y=rnorm(10))

# Define server logic required to draw a histogram
shinyServer(function(input, output) {


  
  # render data selection
  output$cap_table <- DT::renderDataTable(data)

    
    
    # Data download
  observeEvent(input$cap_download, {
    
    shinyalert(title = "Pump the breaks!", 
               text = "Did you get approval for data use from the data owners?",
               type = "input", closeOnClickOutside = T, showCancelButton = T, inputId = "cap_download_btn",
               showConfirmButton = T, confirmButtonText = "Confirm", cancelButtonText = "Cancel", 
               animation = "slide-from-top", inputPlaceholder = "enter_username")
    
  })
  
  observeEvent(input$cap_download_btn,{
    if(input$cap_download_btn %in% credentials$user)
      showModal(modalDialog(downloadButton("cap_dwnld", "Download"), footer = NULL, easyClose = T, size = "s"))
  })
  
  output$cap_dwnld <- downloadHandler(
    filename = function(){"insert_name.csv"},
    
    content = function(file) {
      shiny::withProgress(
        message = paste0("Downloading Capture Data"),
        value = 0,
        {
          shiny::incProgress(3/10)
          Sys.sleep(1)
          shiny::incProgress(9/10)
          write.csv(cap_data(), file, row.names = FALSE)
        }
      )
    }
  )

用户界面

library(shiny)
library(shinyalert)

# Define UI for application that draws a histogram
shinyUI(fluidPage(

    # BUTTON THEMEING - THIS WHERE I NEED HELP
    tags$style(HTML('.alert .confirm {background-color: #2874A6 !important;}')),
    tags$style(HTML('.alert .cancel {background-color: #2874A6 !important;}')),
    tags$style(HTML('.alert .test {background-color: #2874A6 !important;}')),

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins
    sidebarLayout(
        sidebarPanel(
            
        ),

        # Show a plot of the generated distribution
        mainPanel(
          DT::dataTableOutput("cap_table"),
            useShinyalert(),
            actionButton('cap_download',"Download the data")
        )
    )
))