Creating a hexagonical button in shiny

[GreyMerchant]

Hello,

I have this really simple example of shiny below. It creates a circle button instead of the normal one. I am hoping I can convert it to a hexagon. I tried inserting code from here:
http://brenna.github.io/csshexagon/ but not winning (my html and css knowledge is very limited).

1. Can anyone show me how to adjust the code below to get to a hexagonical shaped button?

library(shiny)

ui <- fluidPage(
  tags$head(
    tags$style(HTML("
                  .btn {
                    display:block;
                    height: 60px;
                    width: 60px;
                    border-radius: 50%;
                    border: 1px solid red;

                    }

                    "))
  ),
  actionButton("do", "Go!")
)

server <- function(input, output, session) {
  observeEvent(input$do, {
    print(2)
  })
}

shinyApp(ui, server)

2. In addition, I'd like to know how best to change the properties of the button by a checkboxGroupInput. If say the second item on a list is selected the second custom button changes colour.