hi im kind of new at this forum so please go ez on me 
i want to add Manual Slideshow like it in this link it works but still the prev & next button r not in the right place still dont know how can i put them in the right place
as its showen in the link it should be in middle

i want to add Manual Slideshow like it in this link it works but still the prev & next button r not in the right place still dont know how can i put them in the right place
as its showen in the link it should be in middle
CSS:
@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@100;300;400;500;700&display=swap');
:root{
--main-color:#d3ad7f;
--black:#13131a;
--bg:#010103;
--border:.1rem solid rgba(255,255,255,.3);
}
*{
font-family: 'Roboto', sans-serif;
margin:0; padding:0;
box-sizing: border-box;
outline: none; border:none;
text-decoration: none;
transition: .2s linear;
}
html{
font-size: 62.5%;
overflow-x: hidden;
scroll-padding-top: 9rem;
scroll-behavior: smooth;
}
html::-webkit-scrollbar{
width: .8rem;
}
html::-webkit-scrollbar-track{
background: transparent;
}
html::-webkit-scrollbar-thumb{
background: #fff;
border-radius: 5rem;
}
body{
background: var(--bg);
}
section{
padding:2rem 7%;
}
.heading{
text-align: center;
color:#fff;
text-transform: uppercase;
padding-bottom: 3.5rem;
font-size: 4rem;
}
.heading span{
color:var(--main-color);
text-transform: uppercase;
}
.btn{
margin-top: 1rem;
display: inline-block;
padding:.9rem 3rem;
font-size: 1.7rem;
color:#fff;
background: var(--main-color);
cursor: pointer;
}
.btn:hover{
letter-spacing: .2rem;
}
.header{
background-image: linear-gradient(to right, #9f8282 , #2a323d);
display: flex;
align-items: center;
justify-content: space-between;
padding:1.5rem 7%;
border-bottom: var(--border);
position: fixed;
top:0; left: 0; right: 0;
z-index: 1000;
}
.header .logo img{
height: 6rem;
}
.header .navbar a{
margin:0 1rem;
font-size: 1.6rem;
color:#fff;
}
.header .navbar a:hover{
color:var(--main-color);
border-bottom: .1rem solid var(--main-color);
padding-bottom: .5rem;
}
.header .icons div{
color:#fff;
cursor: pointer;
font-size: 2.5rem;
margin-left: 2rem;
}
.header .icons div:hover{
color:var(--main-color);
}
#menu-btn{
display: none;
}
.header .search-form{
position: absolute;
top:115%; right: 7%;
background: #fff;
width: 50rem;
height: 5rem;
display: flex;
align-items: center;
transform: scaleY(0);
transform-origin: top;
}
.header .search-form.active{
transform: scaleY(1);
}
.header .search-form input{
height: 100%;
width: 100%;
font-size: 1.6rem;
color:var(--black);
padding:1rem;
text-transform: none;
}
.header .search-form label{
cursor: pointer;
font-size: 2.2rem;
margin-right: 1.5rem;
color:var(--black);
}
.header .search-form label:hover{
color:var(--main-color);
}
.header .cart-items-container{
position: absolute;
top:100%; right: -100%;
height: calc(100vh - 9.5rem);
width: 35rem;
background: #fff;
padding:0 1.5rem;
}
.header .cart-items-container.active{
right: 0;
}
.header .cart-items-container .cart-item{
position: relative;
margin:2rem 0;
display: flex;
align-items: center;
gap:1.5rem;
}
.header .cart-items-container .cart-item .fa-times{
position: absolute;
top:1rem; right: 1rem;
font-size: 2rem;
cursor: pointer;
color: var(--black);
}
.header .cart-items-container .cart-item .fa-times:hover{
color:var(--main-color);
}
.header .cart-items-container .cart-item img{
height: 7rem;
}
.header .cart-items-container .cart-item .content h3{
font-size: 2rem;
color:var(--black);
padding-bottom: .5rem;
}
.header .cart-items-container .cart-item .content .price{
font-size: 1.5rem;
color:var(--main-color);
}
.header .cart-items-container .btn{
width: 100%;
text-align: center;
}
.home{
min-height: 100vh;
display: flex;
align-items: center;
background:url(../images/home-img.jpg) no-repeat;
background-size: cover;
background-position: center;
}
.home .content{
max-width: 60rem;
}
.home .content h3{
font-size: 6rem;
text-transform: uppercase;
color:#fff;
}
.home .content p{
font-size: 2rem;
font-weight: lighter;
line-height: 1.8;
padding:1rem 0;
color:#eee;
}
.about .row{
display: flex;
align-items: center;
background:var(--black);
flex-wrap: wrap;
}
.about .row .image{
flex:1 1 45rem;
}
.about .row .image img{
width: 100%;
}
.about .row .content{
flex:1 1 45rem;
padding:2rem;
}
.about .row .content h3{
font-size: 3rem;
color:#fff;
}
.about .row .content p{
font-size: 1.6rem;
color:#ccc;
padding:1rem 0;
line-height: 1.8;
}
.menu .box-container{
display: grid;
grid-template-columns: repeat(auto-fit, minmax(30rem, 1fr));
gap:1.5rem;
}
.menu .box-container .box{
padding:5rem;
text-align: center;
border:var(--border);
}
.menu .box-container .box img{
height: 10rem;
}
.menu .box-container .box h3{
color: #fff;
font-size: 2rem;
padding:1rem 0;
}
.menu .box-container .box .price{
color: #fff;
font-size: 2.5rem;
padding:.5rem 0;
}
.menu .box-container .box .price span{
font-size: 1.5rem;
text-decoration: line-through;
font-weight: lighter;
}
.menu .box-container .box:hover{
background:#fff;
}
.menu .box-container .box:hover > *{
color:var(--black);
}
.products .box-container{
display: grid;
grid-template-columns: repeat(auto-fit, minmax(30rem, 1fr));
gap:1.5rem;
}
.products .box-container .box{
text-align: center;
border:var(--border);
padding: 2rem;
}
.products .box-container .box .icons a{
height: 5rem;
width: 5rem;
line-height: 5rem;
font-size: 2rem;
border:var(--border);
color:#fff;
margin:.3rem;
}
.products .box-container .box .icons a:hover{
background:var(--main-color);
}
.products .box-container .box .image{
padding: 2.5rem 0;
}
.products .box-container .box .image img{
height: 25rem;
}
.products .box-container .box .content h3{
color:#fff;
font-size: 2.5rem;
}
.products .box-container .box .content .stars{
padding: 1.5rem;
}
.products .box-container .box .content .stars i{
font-size: 1.7rem;
color: var(--main-color);
}
.products .box-container .box .content .price{
color:#fff;
font-size: 2.5rem;
}
.products .box-container .box .content .price span{
text-decoration: line-through;
font-weight: lighter;
font-size: 1.5rem;
}
.review .box-container{
display: grid;
grid-template-columns: repeat(auto-fit, minmax(30rem, 1fr));
gap:1.5rem;
}
.review .box-container .box{
border:var(--border);
text-align: center;
padding:3rem 2rem;
}
.review .box-container .box p{
font-size: 1.5rem;
line-height: 1.8;
color:#ccc;
padding:2rem 0;
}
.review .box-container .box .user{
height: 7rem;
width: 7rem;
border-radius: 50%;
object-fit: cover;
}
.review .box-container .box h3{
padding:1rem 0;
font-size: 2rem;
color:#fff;
}
.review .box-container .box .stars i{
font-size: 1.5rem;
color:var(--main-color);
}
.contact .row{
display: flex;
background:var(--black);
flex-wrap: wrap;
gap:1rem;
}
.contact .row .map{
flex:1 1 45rem;
width: 100%;
object-fit: cover;
}
.contact .row form{
flex:1 1 45rem;
padding:5rem 2rem;
text-align: center;
}
.contact .row form h3{
text-transform: uppercase;
font-size: 3.5rem;
color:#fff;
}
.contact .row form .inputBox{
display: flex;
align-items: center;
margin-top: 2rem;
margin-bottom: 2rem;
background:var(--bg);
border:var(--border);
}
.contact .row form .inputBox span{
color:#fff;
font-size: 2rem;
padding-left: 2rem;
}
.contact .row form .inputBox input{
width: 100%;
padding:2rem;
font-size: 1.7rem;
color:#fff;
text-transform: none;
background:none;
}
.blogs .box-container{
display: grid;
grid-template-columns: repeat(auto-fit, minmax(30rem, 1fr));
gap:1.5rem;
}
.blogs .box-container .box{
border:var(--border);
}
.blogs .box-container .box .image{
height: 25rem;
overflow:hidden;
width: 100%;
}
.blogs .box-container .box .image img{
height: 100%;
object-fit: cover;
width: 100%;
}
.blogs .box-container .box:hover .image img{
transform: scale(1.2);
}
.blogs .box-container .box .content{
padding:2rem;
}
.blogs .box-container .box .content .title{
font-size: 2.5rem;
line-height: 1.5;
color:#fff;
}
.blogs .box-container .box .content .title:hover{
color:var(--main-color);
}
.blogs .box-container .box .content span{
color:var(--main-color);
display: block;
padding-top: 1rem;
font-size: 2rem;
}
.blogs .box-container .box .content p{
font-size: 1.6rem;
line-height: 1.8;
color:#ccc;
padding:1rem 0;
}
.footer{
background:var(--black);
text-align: center;
}
.footer .share{
padding:1rem 0;
}
.footer .share a{
height: 5rem;
width: 5rem;
line-height: 5rem;
font-size: 2rem;
color:#fff;
border:var(--border);
margin:.3rem;
border-radius: 50%;
}
.footer .share a:hover{
background-color: var(--main-color);
}
.footer .links{
display: flex;
justify-content: center;
flex-wrap: wrap;
padding:2rem 0;
gap:1rem;
}
.footer .links a{
padding:.7rem 2rem;
color:#fff;
border:var(--border);
font-size: 2rem;
}
.footer .links a:hover{
background:var(--main-color);
}
.footer .credit{
font-size: 2rem;
color:#fff;
font-weight: lighter;
padding:1.5rem;
}
.footer .credit span{
color:var(--main-color);
}
.w3-btn,.w3-button{border:none;display:inline-block;padding:8px 16px;vertical-align:middle;overflow:hidden;text-decoration:none;color:inherit;background-color:inherit;text-align:center;cursor:pointer;white-space:nowrap}
.w3-btn:hover{box-shadow:0 8px 16px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19)}
.w3-btn,.w3-button{-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none}
/* media queries */
@media (max-width:991px){
html{
font-size: 55%;
}
.header{
padding:1.5rem 2rem;
}
section{
padding:2rem;
}
}
@media (max-width:768px){
#menu-btn{
display: inline-block;
}
.header .navbar{
position: absolute;
top:100%; right: -100%;
background: #fff;
width: 30rem;
height: calc(100vh - 9.5rem);
}
.header .navbar.active{
right:0;
}
.header .navbar a{
color:var(--black);
display: block;
margin:1.5rem;
padding:.5rem;
font-size: 2rem;
}
.header .search-form{
width: 90%;
right: 2rem;
}
.home{
background-position: left;
justify-content: center;
text-align: center;
}
.home .content h3{
font-size: 4.5rem;
}
.home .content p{
font-size: 1.5rem;
}
}
@media (max-width:450px){
html{
font-size: 50%;
}
}
HTML:
<section class="about" id="about">
<h1 class="heading"> <span>Over</span> ons</h1>
<div class="row">
<div class="image">
<img class="mySlides" src="images/about-img.jpg">
<img class="mySlides" src="images/about-img1.jpg">
<img class="mySlides" src="images/about-img3.jpg">
<img class="mySlides" src="images/about-img4.jpg">
<button class="w3-button w3-display-left" onclick="plusDivs(-1)">❮</button>
<button class="w3-button w3-display-right" onclick="plusDivs(+1)">❯</button>
</div>
<div class="content">
<h3>Wat maakt onze service speciaal?</h3>
<p>We zijn ervaren met het monteren van alle soorten meubels. (Pax)kasten (met/zonder schuifdeuren), bedden, stoelen, tafels, banken, bureaus, commodes etc.</p>
<p> Ook (de)monteren en vervoeren wij tweedehands meubels. WE ZIJN ALTIJD HET GOEDKOOPST!</p>
<a href="#" class="btn">Meer informatie</a>
</div>
<script>
var slideIndex = 1;
showDivs(slideIndex);
function plusDivs(n) {
showDivs(slideIndex += n);
}
function showDivs(n) {
var i;
var x = document.getElementsByClassName("mySlides");
if (n > x.length) {slideIndex = 1}
if (n < 1) {slideIndex = x.length}
for (i = 0; i < x.length; i++) {
x[i].style.display = "none";
}
x[slideIndex-1].style.display = "block";
}
</script>
</div>
</section>