JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="icon" href="Images/logo-square-letter.png">
    <link rel="stylesheet" href="buds-2.css" type="text/css">
    <link href="https://fonts.googleapis.com/icon?family=Material+Icons" rel="stylesheet">
    <link href="http://fonts.cdnfonts.com/css/samsungone" rel="stylesheet">
    <title>Samsung Galaxy Buds 2</title>
</head>

<body>
  <button id="ScrollToTop">
    <i class="material-icons">arrow_upward</i>
</button>
<script>
    const ScrollToTop = document.querySelector("#ScrollToTop");

    ScrollToTop.addEventListener("click", function () {
        window.scrollTo(0, 0);
    });
</script>
    <header>
        <div class="logo">
            <a href="index.html"><img src="Images/samsung-logo.png" alt="Samsung Logo" width="150"></a>
            <ul class="menubalk">
                <a href="mailto:[email protected]" target="_blank"><li>Contact</li></a>
                <a href="index.html#assortiment"><li>Assortiment</li></a>
            </ul>
        </div>
    </header>

    <div class="product">
      <ul>
        <li id="product-naam"><strong>Galaxy Buds 2</strong></li>
        <a href="#info"><li>test</li></a>
      </ul>
    </div>

  <div class="slideshow-container">
    <div class="mySlides fade">
      <img src="Images/Buds2-1.jpg" width="853">
    </div>

    <div class="mySlides fade">
      <img src="Images/Buds2-2.jpg" width="853">
    </div>

    <div class="mySlides fade">
      <img src="Images/Buds2-3.jpg" width="853">
    </div>

    <a class="prev" onclick="plusSlides(-1)">&#10094;</a>
    <a class="next" onclick="plusSlides(1)">&#10095;</a>
  </div>
  <br>
  <br>
  <div class="specs">
    <h1 class="cat">Audio</h1>
    <ul class="info">
      <li>Diameter</li>
      <li>18mm</li>
    </ul>
  </div>
</body>

</html>

CSS

html {
    scroll-behavior: smooth;
    overflow-x: hidden
}
body {
  font-family: 'SamsungOne', sans-serif;
}
a{
    color: black;
    text-decoration: none;
}
.product {
  position: absolute;
  margin-top: 25px;
  display: flex;
  flex-direction: row;
  color: black;
}
.product ul {
  display: flex;
  flex-direction: row;
  align-items: center;
  font: 50;
}
.product li {
  display: flex;
  flex-direction: row;
  margin-right: 50px;
}
.product ul #product-naam{
  font-size: xx-large;
  margin-left: -10px;
}
#ScrollToTop{
  position: fixed;
  right: 25px;
  bottom: 55px;
  width: 60px;
  height: 60px;
  border-radius: 50%;
  background-color: black;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.25);
  color: white;
  outline: none;
  border: none;
  cursor: pointer;
  z-index: 1;
}
#ScrollToTop:hover{
  background: white;
  color: black;
}
.logo {
  position: relative;
  top: 20px;
  left: 30px;
  display: flex;
  flex-direction: row;
  align-items: center;
}
.menubalk {
  display: flex;
  flex-direction: row;
  color: black;
  align-items: center;
}
.menubalk li {
  display: flex;
  flex-direction: row;
  margin-right: 50px;
}
.name{
  position: absolute;
  margin-top: 100px;
}
.slideshow-container {
  max-width: 853px;
  position: relative;
  margin: auto;
}
.mySlides {
  display: none;
}
.prev, .next {
  cursor: pointer;
  position: absolute;
  top: 50%;
  width: auto;
  margin-top: -22px;
  padding: 16px;
  color: black;
  font-weight: bold;
  font-size: 18px;
  transition: 0.6s ease;
  border-radius: 0 3px 3px 0;
  user-select: none;
}
.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}
.prev:hover, .next:hover {
  background-color: rgba(0, 0, 0, 0.411);
}
.fade {
  animation-name: fade;
  animation-duration: 1s;
}
@keyframes fade {
  from {opacity: .7}
  to {opacity: 1}
}
.achtergrond{
  background-color: black;
  color: white;
  display: block;
  box-sizing: border-box;
}
.specs{
  position: relative;
  top: 20px;
  display: flex;
  flex-direction: row;
 ...

JavaScript

let slideIndex = 1;
    showSlides(slideIndex);

    function plusSlides(n) {
      showSlides(slideIndex += n);
    }

    function currentSlide(n) {
      showSlides(slideIndex = n);
    }

    function showSlides(n) {
      let i;
      let slides = document.getElementsByClassName("mySlides");
      let dots = document.getElementsByClassName("dot");
      if (n > slides.length) { slideIndex = 1 }
      if (n < 1) { slideIndex = slides.length }
      for (i = 0; i < slides.length; i++) {
        slides[i].style.display = "none";
      }
      for (i = 0; i < dots.length; i++) {
        dots[i].className = dots[i].className.replace(" active", "");
      }
      slides[slideIndex - 1].style.display = "block";
      dots[slideIndex - 1].className += " active";
    }