Countdown when trigger is pressed

I've got a 2-Digit seven segment display that i want to count down from 99 to 00 when i pull a trigger.

I've used this code and library: Arduino and 2-Digit Seven Segment Module - Ardumotive Arduino Greek Playground
and modified it.

I get as far as starting the counddown with the trigger, but it doeesn't paus when the trigger is released.
I need it to just pause and not reset.

BONUS:
If at all possible i would like it to count faster, and restart from 99 when it has reached 00 as well.

#include <ShiftRegister74HC595.h>
// create shift register object (number of shift registers, data pin, clock pin, latch pin)
ShiftRegister74HC595 sr (2, 2, 3, 4);

int number = 99; // <--- Change it from 0 to 99

int value, digit1, digit2, digit3, digit4;
uint8_t  numberB[] = {B11000000, //0
                      B11111001, //1
                      B10100100, //2
                      B10110000, //3
                      B10011001, //4
                      B10010010, //5
                      B10000011, //6
                      B11111000, //7
                      B10000000, //8
                      B10011000 //9
                     };

const int trigger = 3;     // the number of the trigger pin
const int boxled =  5;      // the number of the box LED pin to the display
int buttonState = 0;         // variable for reading the pushbutton status
void setup() {
  pinMode(boxled, OUTPUT);
  pinMode(trigger, INPUT);

}

void loop()
{ buttonState = digitalRead(trigger);
  if (buttonState == HIGH)
    countDown();
}
// else
// countdown pauses when trigger is released and resumes when pressed again



void countDown() {
  for (number; number >= 0; number--) {
    //Split number to digits:
    digit2 = number % 10 ;
    digit1 = (number / 10) % 10 ;
    //Send them to 7 segment displays
    uint8_t numberToPrint[] = {numberB[digit2], numberB[digit1]};
    sr.setAll(numberToPrint);
    //Reset them for next time
    digit1 = 0;
    digit2 = 0;
    delay(1000); // Repeat every 1 sec
  }
}

Let the loop() do the looping. Remove the for-loop and add the number-- the end of the function.

To go from 99 to 0 change:

//from this
number--;

//to this:
if(number == 0){
  number = 99;
}
else{
  number--;
}