Question: Having trouble for adding a gradient color to my fileinput progress bar. 

Right now, I was able to change the color of the progress bar from a regular blue to something else using the code provided here. [Colour of progress bar in fileInput -- Shiny](https://stackoverflow.com/questions/44401763/colour-of-progress-bar-in-fileinput-shiny)

```
ui <- fluidPage(

    tags$head(tags$style(".progress-bar{background-color:#3c763d;}")),

    fileInput(inputId = "fileInp", label = "Input file:",multiple = FALSE,
               accept = c(
                 "text/csv",
                 "text/comma-separated-values,text/plain",
                 ".csv"))

  )

  server <- function(input, output){

  }

  shinyApp(ui=ui, server=server)

##also tried replacing background color with code from https://www.w3schools.com/css/css3_gradients.asp but no luck :

  background-color: linear-gradient(to right, red , yellow);

```

However, what I want is to have gradient just like this <https://imgur.com/XdFBUIt>

Answer: 
To set a gradient in CSS, the property is `background-image`, not `background-color`. You also have to set the `background-size` to `auto`, otherwise it is set to `40px 40px` and the progress bar is striped. Here is the CSS:

```
  tags$head(
    tags$style(
      ".progress-bar {
          background-image: linear-gradient(to right, red , yellow) !important;
          background-size: auto !important;
      }")
  )

```
Try creating a colour ramp from a predefined color palette:
 <https://www.rdocumentation.org/packages/dichromat/versions/1.1/topics/colorRampPalette>