Change dynamic textbox background colour

Any ideas how to make the text box display a background? The font changes but the background doesn't.

 if (displayedItem === _this.display.text) { 
     textBox.text = `${displayedItem} ${fuelOrder}`;     
  	 textBox.font = "23px Arial" // THIS WORKS
         textBox.background=true;
	 textBox.backgroundColor = "#00ff00";

Thanks!