Progressing bar in Showmodal function

Hi all,

Below is the sample of code where I have incorporated showmodal at the top once the button is pressed. But wanted to check if there is a way to put showmodal in the center of the screen and also instead of just a message, can we have progressing bar (in showmodal function itself)

observeEvent(input$button, {
     showModal(modalDialog("Doing a function", footer=NULL))
     #Do the stuff here....
     #...
     #...
     #Finish the function
     removeModal()
})