app.js

let numberContainer = document.getElementById("number");
let value = 0;

let btnIncrease = document.querySelector(".increase");
let btnDecrease = document.querySelector(".decrease");
let btnReset = document.querySelector(".reset");


btnIncrease.addEventListener("click", () => {
    value++;

    value % 10 === 0
        ? (numberContainer.style.color = "#8c3c23")
        : (numberContainer.style.color = "#406485");

    numberContainer.textContent = value;
});

btnDecrease.addEventListener("click", () => {

    value--;

    if (value < 0) {
        value = 0;
        alert("The number cannot be less than zero.");
    }

    value % 10 === 0
        ? (numberContainer.style.color = "#8c3c23")
        : (numberContainer.style.color = "#406485");

    numberContainer.textContent = value;
});

btnReset.addEventListener("click", () => {
    value = 0;
    numberContainer.textContent = value;
});