Text centered in progress bar

I have a Formula Rich text field set up that works as a progress bar - here is the formula:

var text redbox = "https://lamresearch.quickbase.com/up/bpcve39mm/g/rd/eg/va/red.png";  // red 
var text yellowbox = "https://lamresearch.quickbase.com/up/bpcve39mm/g/re/eg/va/orange.png"; // yellow
var text greenbox = "https://lamresearch.quickbase.com/up/bpcve39mm/g/rf/eg/va/green.png"; // green
var text graybox = "https://lamresearch.quickbase.com/up/bpcve39mm/g/rg/eg/va/grey.png"; // gray

var text box = If([Feeder Line %]<0.4,$redbox, If([Feeder Line %]<0.7,$yellowbox,$greenbox));
var text widthval ="\"" &Min(Max([Feeder Line %]*100,0),100)&"\"";
var text widthvalbalance ="\"" &ToText(Max(0,Min(100,100-([Feeder Line %]*100))))&"\"";
"<img height = 18 width="&$widthval & "src=\""&$box&"\"/>" &"<img height = 18 width="&$widthvalbalance&"src=\""&$graybox&"\"/>"


I want to display the % (Feeder Line %]*100) centered in this progress bar, where/how would I go about doing this?