<body>
  <div class="container">
    <div class="product">
      
    </div>
    <div class="pricing">
      <p>
        <span class="price">100</span>
        <span class="currency">$</span>
      </p>
      <div class="custom">
        <button class="btn add">&plus;</button>
        <button class="btn remove">&minus;</button>
      </div>
      <div class="add-to-cart">
        <p>
          <span class="quantity">1</span>
            item to buy
          </p>
        <button class="buy-btn">Add To Card</button>
      </div>
    </div>
  </div>
</body>
*,
*::after,
*::before{
  margin: 0;
  paddin: 0;
  box-sizing: border-box;
  font-family: sans-serif
}
body{
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center
}
.container{
  display: flex;
  align-items: center;
  gap: 2rem
}
.product{
  width: 100px;
  height: 150px;
  background: rgba(0,0,0,.2);
  border-radius: 10px;
}
.pricing{
  text-align: center;
}
.pricing p{
  font-size: 3rem;
  font-weight: bold
}
.custom {
  margin-bottom: 20px;
}
.custom button{
  padding: .8em;
}
.buy-btn{
  padding: .5em 1em;
  background: orange;
  border: none
}
button{
  cursor: pointer;
}

@media(max-width: 400px) {
  .container{
    flex-direction: column
  }
}
function _s(element, all) { 
  if(all) {
    return document.querySelectorAll(element)
  }
  return document.querySelector(element);
}

let price = _s(".price").textContent,
    buttons = _s(".btn", true),
    quantity = _s(".quantity"),
    items = parseInt(quantity.textContent);

buttons.forEach(button => {
  button.addEventListener("click", function(e) {
    if(e.target.classList.contains("add")) {
      items++
    } else {
      if(items > 1) items--
    }
    
    _s(".price").textContent = +price * items;
    quantity.textContent = items;
  })
})

External CSS

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External JavaScript

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