HTML ve CSS'in yanı sıra JavaScript kullanmanız gerek.

HTML
<div class="product-options">
    <div class="sizes">
        <button class="size-btn" data-stock="1 Ürün!">36</button>
        <button class="size-btn" data-stock="5 Ürün!">37</button>
        <button class="size-btn" data-stock="2 Ürün!">38</button>
        <button class="size-btn" data-stock="0 Ürün!">39</button>
        <button class="size-btn" data-stock="Tükendi" disabled>40</button>
    </div>
    <div id="stock-info"></div>
</div>
CSS
.size-btn {
    margin: 5px;
    padding: 10px;
    border: 1px solid #000;
    background-color: #fff;
    cursor: pointer;
}

.size-btn:disabled {
    background-color: #ccc;
    cursor: not-allowed;
}

#stock-info {
    margin-top: 20px;
    font-weight: bold;
    color: red;
}
JAVASCRIPT
document.addEventListener('DOMContentLoaded', function() {
    const buttons = document.querySelectorAll('.size-btn');
    const stockInfo = document.getElementById('stock-info');

    buttons.forEach(button => {
        button.addEventListener('click', function() {
            const stock = this.getAttribute('data-stock');
            stockInfo.textContent = `Beden: ${this.textContent} - Stok Durumu: ${stock}`;
        });
    });
});
Mantığını kavramak için alttaki kodları bu sitede ilgili yerlere yapıştırabilirsiniz.

HTML
<!DOCTYPE html>
<html lang="tr">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Ayakkabı Stok Durumu</title>
    <link rel="stylesheet" href="styles.css">
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    <link href="https://fonts.googleapis.com/css2?family=Roboto:wght@400;500;700&display=swap" rel="stylesheet">
</head>
<body>
    <div class="container">
        <div class="product">
            <div class="product-images">
                <img src="https://via.placeholder.com/300x300" alt="Shoe 1" class="product-image">
                <img src="https://via.placeholder.com/300x300" alt="Shoe 2" class="product-image">
                <img src="https://via.placeholder.com/300x300" alt="Shoe 3" class="product-image">
            </div>
            <div class="product-info">
                <h1>Ayakkabı Modeli</h1>
                <p class="price">₺333,00 'den başlayan fiyatlarla</p>
                <div class="sizes">
                    <h2>Beden Seçenekleri</h2>
                    <button class="size-btn" data-stock="1 Ürün!">36</button>
                    <button class="size-btn" data-stock="5 Ürün!">37</button>
                    <button class="size-btn" data-stock="2 Ürün!">38</button>
                    <button class="size-btn" data-stock="0 Ürün!">39</button>
                    <button class="size-btn" data-stock="Tükendi" disabled>40</button>
                </div>
                <div id="stock-info">Stok Durumunu Görmek İçin Beden Seçin</div>
                <div class="color-options">
                    <h2>Renk</h2>
                    <button class="color-btn" style="background-color: #FFFFFF;">Bordo</button>
                    <button class="color-btn" style="background-color: #FFFFFF;">Siyah</button>
                    <button class="color-btn" style="background-color: #FFFFFF;">Beyaz</button>
                </div>
                <div class="add-to-cart">
                    <label for="quantity">Adet:</label>
                    <input type="number" id="quantity" name="quantity" min="1" value="1">
                    <button id="add-to-cart-btn">Sepete Ekle</button>
                </div>
            </div>
        </div>
    </div>
    <script src="scripts.js"></script>
</body>
</html>
CSS
body {
    font-family: 'Roboto', sans-serif;
    background-color: #f4f4f4;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.container {
    background-color: #fff;
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.1);
    max-width: 800px;
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
}

.product {
    width: 100%;
}

.product-images {
    display: flex;
    justify-content: center;
    gap: 15px;
    margin-bottom: 20px;
}

.product-image {
    width: 100px;
    height: 100px;
    object-fit: cover;
    border-radius: 8px;
    border: 1px solid #ddd;
    transition: transform 0.3s;
}

.product-image:hover {
    transform: scale(1.1);
}

.product-info h1 {
    font-size: 24px;
    margin-bottom: 10px;
}

.product-info .price {
    font-size: 20px;
    color: #888;
    margin-bottom: 20px;
}

.sizes, .color-options {
    margin: 20px 0;
}

.size-btn, .color-btn {
    margin: 5px;
    padding: 10px 20px;
    border: 1px solid #000;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s, color 0.3s;
}

.size-btn:hover, .color-btn:hover {
    background-color: #ddd;
}

.size-btn:disabled {
    background-color: #ccc;
    cursor: not-allowed;
}

#stock-info {
    margin-top: 20px;
    font-weight: bold;
    color: red;
}

.add-to-cart {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 10px;
    margin-top: 20px;
}

#quantity {
    width: 60px;
    padding: 8px;
    border: 1px solid #ddd;
    border-radius: 5px;
    text-align: center;
}

#add-to-cart-btn {
    padding: 10px 20px;
    background-color: #000;
    color: #fff;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s;
}

#add-to-cart-btn:hover {
    background-color: #444;
}
document.addEventListener('DOMContentLoaded', function() {
    const sizeButtons = document.querySelectorAll('.size-btn');
    const stockInfo = document.getElementById('stock-info');
    const addToCartBtn = document.getElementById('add-to-cart-btn');
    const quantityInput = document.getElementById('quantity');

    sizeButtons.forEach(button => {
        button.addEventListener('click', function() {
            const stock = this.getAttribute('data-stock');
            stockInfo.textContent = `Beden: ${this.textContent} - Stok Durumu: ${stock}`;
            sizeButtons.forEach(btn => btn.classList.remove('selected'));
            this.classList.add('selected');
        });
    });

    addToCartBtn.addEventListener('click', function() {
        const selectedSize = document.querySelector('.size-btn.selected');
        if (selectedSize) {
            const size = selectedSize.textContent;
            const quantity = quantityInput.value;
            alert(`${quantity} adet ${size} numara ayakkabı sepete eklendi!`);
        } else {
            alert('Lütfen bir beden seçin.');
        }
    });
});