arduino count down

#include <Wire.h>
#include<I2Cdev.h>
#include <Adafruit_SH1106.h>
#include <Adafruit_GFX.h>
Adafruit_SH1106 oled(4);
int led = 9;
int counter = 0;
bool on = false;
int d8 = 8;
int d7 = 7;
void setup() {

  pinMode(led, OUTPUT);
  pinMode(d8, INPUT_PULLUP);
  pinMode(d7, INPUT_PULLUP);
  oled.begin(SH1106_SWITCHCAPVCC, 0x3C);
  oled.clearDisplay();
  oled.setTextSize(1);
  oled.setTextColor(WHITE);

}
void loop() {
  oled.setCursor(10, 10);
  oled.print("delay =");
  if (digitalRead(d7) == LOW) {
    counter += 1;
    
  }

    oled.setCursor(70, 10);
    oled.print(counter);
   
  if (digitalRead(d8) == LOW) {
    if (on == true) {
      on = false;

    }  else {
      on = true;
    }
  }
  delay(100);
  if (on == true) {
    counter -= 1;

    if (counter == 1) {
      analogWrite(led, 200);
    }
    if (counter < 1) {
      counter = 1;
    }
    oled.setCursor(30, 40);
    oled.print("C = ");
    oled.setCursor(50, 40);
    oled.print(counter);
    oled.display();
  }
  oled.display();
  oled.clearDisplay();

}