R Shiny dropdownButton reactive size?

I'm using the dropdownButton from this link that is in Shiny Widgets, with a slight mod to make the text black. drop-down checkbox input in shiny

My goal is to make the dropdownButton in my sidebar look as much like a selectInput feature as possible. I got the button to be the same size as the the selectInput, and the caret to be placed correctly, thanks to help on another post, but when I change the window size, I run into UI overlap issues.

Any suggestions? See my issue below:

Both are screenshots of the same app from the same code, just different window sizes. I'd like the dropdownButton to stay consistent in matching its size to the selectInput above. I also don't understand why my h5("Filter 2:) text splits with the larger window size, and I don't want it to do that.

library(shiny)
library(shinydashboard)


dropdownButton2 <- function(label = "", status = c("default", "primary", "success", "info", "warning", "danger"), ..., width = NULL) {

  status <- match.arg(status)
  # dropdown button content
  html_ul <- list(
    class = "dropdown-menu",
    style = if (!is.null(width)) 
      paste0("width: ", validateCssUnit(width), ";"),
    lapply(X = list(...), FUN = tags$li, style = "margin-left: 10px; margin-right: 10px;color:black")
  )
 # dropdown button apparence
 html_button <- list(
    class = paste0("btn btn-", status," dropdown-toggle"),
    type = "button", 
    `data-toggle` = "dropdown"
  )
  html_button <- c(html_button, list(label))
  html_button <- c(html_button, list(tags$span(class = "caret")))
  # final result
  tags$div(
    class = "dropdown",
    do.call(tags$button, html_button),
    do.call(tags$ul, html_ul),
    tags$script(
      "$('.dropdown-menu').click(function(e) {
      e.stopPropagation();
});")
  )
  }

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(width = 325,
               selectInput('month',label='Filter 1:',choices= month.name,multiple = FALSE,selected = "March"),
               br(),
               column(1,
                      h5(strong(("Filter 2:"))),
                      tags$style(type = 'text/css', ".btn-default{width: 100%;}"),
                      tags$style(type = 'text/css', ".btn .caret{position: relative;}"),
                      tags$style(type = 'text/css', ".caret{top: 45%; right:-35%}"),
                      dropdownButton2(
                        label = "Filter 2:", status = "default", width = 200,#circle = FALSE,
                        checkboxGroupInput(inputId = "check1", label = "Choose", choices = c("A","B","C"))
                      ),
                      h5(strong(("Filter 3:"))),
                      dropdownButton2(
                        label = "Filter 3:", status = "default", width = 200,#circle = FALSE,
                        checkboxGroupInput(inputId = "check3", label = "Choose", choices = c("A","B","C"))
                      )
               )),
  dashboardBody()         
)

server <- function(input, output){
}


shinyApp(ui = ui, server = server)