<div class="container">
  <div class="progress-container">
    <div class="progress" id="progress"></div>
    <div class="circle active"> 1 </div>
    <div class="circle"> 2 </div>
    <div class="circle"> 3 </div>
    <div class="circle"> 4 </div>
  </div>
  <button class="btn" id="prev" disabled> Prev </button>
  <button class="btn" id="next"> Next </button>
</div>

@import url("https://fonts.googleapis.com/css2?family=Muli&display=swap");

:root {
  --line-border-fill: #6f77ec;
  --line-border-empty: #e0e0e0;
}

* {
  box-sizing: border-box;
}

body {
  align-items: center;
  display: flex;
  font-family: "Muli", sans-serif;
  height: 100vh;
  justify-content: center;
  margin: 0;
  overflow: hidden;
}

.container {
  text-align: center;
}

.progress-container {
  display: flex;
  justify-content: space-between;
  position: relative;
  margin-bottom: 30px;
  max-width: 100%;
  width: 350px;
}

.progress-container::before {
  content: "";
  background-color: var(--line-border-empty);
  position: absolute;
  top: 50%;
  left: 0;
  transform: translateY(-50%);
  height: 4px;
  width: 100%;
  z-index: -1;
  transition: 0.4s ease;
}

.progress {
  background-color: var(--line-border-fill);
  position: absolute;
  top: 50%;
  left: 0;
  transform: translateY(-50%);
  height: 4px;
  width: 0%;
  z-index: -1;
  transition: 0.4s ease;
}

.circle {
  background-color: #ffffff;
  color: #999999;
  border-radius: 50%;
  height: 30px;
  width: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 3px solid var(--line-border-empty);
  transition: 0.4s ease;
}

.circle.active {
  border-color: var(--line-border-fill);
}

.btn {
  background-color: var(--line-border-fill);
  color: #000000;
  border: 0;
  border-radius: 6px;
  cursor: pointer;
  font-family: inherit;
  padding: 8px 30px;
  margin: 5px;
  font-size: 14px;
}

.btn:active {
  transform: scale(0.98);
}

.btn:focus {
  outline: 0;
}

.btn:disabled {
  background-color: var(--line-border-empty);
  cursor: not-allowed;
}

const progress = document.getElementById("progress");
const prev = document.getElementById("prev");
const next = document.getElementById("next");
const circles = document.querySelectorAll(".circle");
const themeColor = document.getElementById("theme__color");

let currentActive = 1;

next.addEventListener("click", () => {
  currentActive++;

  if (currentActive > circles.length) {
    currentActive = circles.length;
  }

  update();
});

prev.addEventListener("click", () => {
  currentActive--;

  if (currentActive < 1) {
    currentActive = 1;
  }

  update();
});

function update() {
  circles.forEach((circle, index) => {
    if (index < currentActive) {
      circle.classList.add("active");
    } else {
      circle.classList.remove("active");
    }
  });

  const actives = document.querySelectorAll(".active");
  progress.style.width =
    ((actives.length - 1) / (circles.length - 1)) * 100 + "%";

  //  if (currentActive === 1) {
  //    prev.disabled = true;
  //  } else if (currentActive === circles.length) {
  //    next.disabled = true;
  //  } else {
  //    prev.disabled = false;
  //    next.disabled = false;
  //  }

  if (currentActive === 1) {
    themeColor.setAttribute("content", "#123456");
    prev.disabled = true;
    next.disabled = false;
  } else if (currentActive === 2) {
    themeColor.setAttribute("content", "#ff3366");
    prev.disabled = false;
  } else if (currentActive === 3) {
    themeColor.setAttribute("content", "#0099ff");
    prev.disabled = false;
  } else if (currentActive === circles.length) {
    themeColor.setAttribute("content", "#EF38D6");
    next.disabled = true;
  } else {
    themeColor.setAttribute("content", "#123456");
    prev.disabled = false;
    next.disabled = false;
  }
}