Retain formatting on a PDF output from Shiny downloadHandler

...Is there a way to retain formatting you create in a rmarkdown document when exporting through the downloadHandler functionality? I have created an app that accepts a user input file and after they click process it will create an output. I want that output in pdf format but need to move towards our brand's fonts, colors, etc. While I can change things in the markdown file when downloading the formatting disappears. Any help would be greatly appreciated as to best approaches.

ui <- fluidPage(
  tags$head(
    tags$style("label{font-family: Arial;}")
  ),
    tabPanel("Proposed Lineups",
         fluidRow(
           column(6,
                  tags$br(),
                  fileInput("lineups","Select Input File", 
                            accept = c(".csv",".xlsx")),
                  radioButtons(inputId = 'filetype',label = 'Choose Ticker File Type:',
                               choices = list('CSV ','XLSX'), inline = TRUE)
           ),
           column(6,
                  tags$br(),
                  tags$br(),
                  actionButton("golineup","Create Proposal Summary:",class = "butt"),br(),
                  tags$head(tags$style(".butt{background-color:rgb(85,114,138);} .butt{color: #e6ebef;}")),
                  tags$br(),
                  tags$br(),
                  
                  downloadButton('describe_download',"Download Report",class="butt" ),br(),
                  tags$head(tags$style(".butt{background-color:rgb(85,114,138);} .butt{color: #e6ebef;}")),
                  radioButtons('format', 'Document format', c('Word','PDF'),
                               inline = TRUE)
                  )
         ),
         
         fluidRow(style = "border-bottom: 6px solid; border-color: rgb(85,114,138)",   
                  tags$br()
         ),
         fluidRow(   
           tags$br()
         ),
         DT::dataTableOutput("Lineups")))

server <- function(input,output,session){
  
  #Download the Final Output
  output$describe_download = downloadHandler(
    filename<- function(){
      paste("Summary",Sys.Date(),switch(
        input$format, PDF = '.pdf', Word = '.docx'
      ),sep = "")
    },
    content = function(file) {
      if (input$format=="PDF"){
        #### Progressing indicator
        withProgress(message = 'Download in progress',
                     detail = 'This may take a while...', value = 0, {
                       for (i in 1:15) {
                         incProgress(1/15)
                         Sys.sleep(0.01)
                       }
                       
                       ## End of progression
                       src <- normalizePath("S:/Aaron/R/Apps/Sample Illustrative Lineup Application/summary_PDF.Rmd")
                       
                       # temporarily switch to the temp dir, in case you do not have write
                       # permission to the current working directory
                       owd <- setwd(tempdir())
                       on.exit(setwd(owd))
                       file.copy(src,"summary_PDF.Rmd", overwrite = TRUE)
                       
                       library(rmarkdown)
                       out <- render("summary_PDF.Rmd", pdf_document())
                       file.rename(out, file)
                       
                     })
        ### below is the end of pdf content
      }else{
        withProgress(message = 'Download in progress',
                     detail = 'This may take a while...', value = 0, {
                       for (i in 1:15) {
                         incProgress(1/15)
                         Sys.sleep(0.01)
                       }
                       
                       ## End of progression
                       src <- normalizePath('S:/Aaron/R/Apps/Sample Illustrative Lineup Application/summary_word.Rmd')
                       
                       # temporarily switch to the temp dir, in case you do not have write
                       # permission to the current working directory
                       owd <- setwd(tempdir())
                       on.exit(setwd(owd))
                       file.copy(src, 'summary_word.Rmd', overwrite = TRUE)
                       
                       library(rmarkdown)
                       out <- render('summary_word.Rmd', word_document())
                       file.rename(out, file)
                     })
      }
      
    })
} 


shinyApp(ui = ui, server = server)

#Markdown file I am feeding
---
title: "Sample Proposal -"
author: "`XXXXX`"
date: "`r format(Sys.time(), '%d %B, %Y')`"
output: 
  pdf_document:
    latex_engine: xelatex
mainfont: Arial
allow_html: yes  
---

{r setup, include=FALSE}
knitr::opts_chunk$set(echo = F)

## Proposal Summary
Some text goes here

Code will go below

I think this is happening because of the way you're calling rmarkdown::render():

render("summary_PDF.Rmd", pdf_document())

If you change that to render("summary_PDF.Rmd", "pdf_document") does the problem go away?