TheSanches,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.slider{
position: relative;
}
.slider__container{
white-space: nowrap;
overflow: hidden;
max-width: 790px;
margin: 0 auto;
border: 1px solid #0000FF;
}
.slider__scroll{
position: relative;
left: 0;
transform: translateX(0);
transition: all 0.4s ease-in-out;
display: inline-block;
white-space: nowrap;
}
.slider__item{
display: inline-block;
margin: 0 30px;
width: 300px;
height: 100px;
background-color: #FF1493;
}
.slider__item:nth-child(2){
width: 500px;
background-color: #32CD32;
}
.slider__dots-item{
width: 13px;
height: 13px;
border: 1px solid black;
display: inline-block;
border-radius: 50%;
margin-right: 5px;
cursor: pointer;
transition: all 0.4s;
}
.slider__dots-item.slider__dots-item_active{
background: black;
transition: all 0.4s;
}
.slider__dots-item:last-child{
margin-right: 0;
}
.slider__dots-item:hover{
background: black;
}
</style>
</head>
<body>
<div class="slider">
<div class="slider__btn slider__btn_left">left</div>
<div class="slider__btn slider__btn_right">right</div>
<div class="slider__container">
<div class="slider__scroll">
<div class="slider__item">1</div>
<div class="slider__item">2</div>
<div class="slider__item">3</div>
</div>
</div>
<div class="slider__dots">
<span class="slider__dots-item slider__dots-item_active"></span>
<span class="slider__dots-item"></span>
<span class="slider__dots-item"></span>
</div>
</div>
<script>
var sliderBtnLeft=document.querySelector('.slider__btn_left');
var sliderBtnRight=document.querySelector('.slider__btn_right');
var sliderDots = document.querySelectorAll('.slider__dots-item'); //кружочки
var sliderItems=document.querySelectorAll('.slider__item');
var sliderIndex=0;
var sliderScroll=document.querySelector('.slider__scroll');
var Width=0;
function sliderMove(up)
{
sliderDots[sliderIndex].classList.remove('slider__dots-item_active');
sliderIndex=(sliderIndex + up + sliderItems.length)% sliderItems.length;
sliderDots[sliderIndex].classList.add('slider__dots-item_active');
Width=0;
for(var i=0;i < sliderIndex;i++)
{
Width +=sliderItems[i].offsetWidth + 60
}
sliderScroll.style.transform='translateX(-' + Width + 'px)';
}
function dotMove(i)
{
sliderMove(i - sliderIndex);
}
[...sliderDots].forEach((dot, i) => dot.addEventListener('click', dotMove.bind(dot, i)));
sliderBtnRight.onclick=sliderMove.bind(null,1);
sliderBtnLeft.onclick=sliderMove.bind(null,-1);
</script>
</body>
</html>