Let's start with the things to add to the ui.R. Once again, we add a place for the text to live to the graph tab:

tabPanel("Trend", plotOutput("trend"),
         h3("User selection history"),
         p(id = "selection", ""))

Then, we add a button to add the text and some controls to the sidebar:

actionButton("buttonClick", "Add inputs"),
 
  selectInput("color", "Text colour", 
              c("Red" = "red", 
                "Blue" = "blue", 
                "Black" = "black")),
 
  selectInput("size", "Text size",
              c("Extremely small" = "xx-small", 
                "Very small" = "x-small",
                "Small" = "small", 
                "Medium" = "medium", 
                "Large" = "large", 
                "Extra large" = "x-large", 
                "Super size" = "xx-large"))

The last addition is a reference to the JavaScript file that will make everything happen. We add this with the extendShinyjs() function. Put it underneath useShinyjs(), so you don't lose it:

useShinyjs(),
extendShinyjs(script = "appendText.js")

Let's look now at the server.R code.