pause SevSeg counter timer using push button

i am using bounce2 & SevSeg Libraries on arduino nano v3

push button is connected at analog A1 (15th pin)

i want to use push button to start or pause countdown from 60 to 0
when i press push button then timer can start. when i again press push button then it can pause seven segment digits but it still counting at background.

#include "SevSeg.h"
#include <Bounce2.h>
#define BUTTON_PIN 15
#define LED_PIN 13
int ledState = LOW;
SevSeg sevseg; //Instantiate a seven segment controller object
Bounce debouncer = Bounce();
void setup() {


  byte numDigits = 4;
  byte digitPins[] = {2, 3, 4, 5};
  byte segmentPins[] = {6, 7, 8, 9, 10, 11, 12, 13};

  sevseg.begin(COMMON_ANODE, numDigits, digitPins, segmentPins);
  sevseg.setBrightness(90);


  pinMode(BUTTON_PIN, INPUT_PULLUP);

  // After setting up the button, setup the Bounce instance :
  debouncer.attach(BUTTON_PIN);
  debouncer.interval(500);

  // Setup the LED :
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, ledState);
}

void loop() {
  debouncer.update();

  // Call code if Bounce fell (transition from HIGH to LOW) :
  if ( debouncer.fell() ) {

    // Toggle LED state :
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState);
  }

  pinMode(13, OUTPUT);
  pinMode(18, OUTPUT);
  pinMode(19, OUTPUT);
  digitalWrite(18, LOW);
  digitalWrite(19, HIGH);
  int value = debouncer.read();



  static unsigned long timer = millis();
  static int deciSeconds = 60;
  if ( ledState == HIGH ) {
    if (millis() >= timer) {
      deciSeconds--; // 100000 milliSeconds is equal to 1 Min
      timer += 1000;
      //    digitalWrite(13, HIGH);
      if (deciSeconds <= 0) { // Reset to 0 after counting for 1000 seconds.
        deciSeconds = 0;
        //  digitalWrite(13, LOW);
      }
      sevseg.setNumber(deciSeconds, 1);
    }

    sevseg.refreshDisplay(); // Must run repeatedly
  }
  else {
    deciSeconds;
    timer ;
    sevseg.setNumber(deciSeconds, 1);
    sevseg.refreshDisplay(); // Must run repeatedly
    //   digitalWrite(13, LOW);

  }
  }

  /// END ///