Drivers are concerned with the mileage obtained by their automobiles. One driver has kept track of several tankfuls of gasoline by recording the number of miles driven and the number of gallons used for each tankful. Develop a script that will take as input the miles driven and gallons used (both as integers) for each tankful. The script should calculate and output HTML5 text that displays the number of miles per gallon obtained for each tankful and the combined number of miles per gallons obtained for all tankfuls up to this point. Use prompt dialogs to obtain the data from the user.

Note: The "combined number of miles per gallon obtained for all tankfuls up to this point" is the total miles driven divided by the total gallons used.