```css
/* =========================================
   PRODUCT DETAIL - FULLY RESPONSIVE
   Mobile → Tablet → Desktop → Large LED
========================================= */

.product-detail {
    width: 100%;
    max-width: 1400px;
    margin: 0 auto 50px;

    display: flex;
    align-items: stretch;

    gap: 40px;

    background: #fff;
    border: 1px solid var(--border);
    border-radius: 10px;

    padding: 30px;

    flex-wrap: wrap;

    box-sizing: border-box;
    overflow: hidden;
}


/* =========================================
   PRODUCT IMAGE
========================================= */

.detail-img {
    flex: 1 1 45%;
    min-width: 280px;

    min-height: 320px;

    background: var(--green-light);
    border-radius: 10px;

    display: flex;
    align-items: center;
    justify-content: center;

    overflow: hidden;
    box-sizing: border-box;
}

.detail-img img {
    width: 100%;
    height: 100%;
    min-height: 320px;

    object-fit: cover;
    display: block;
}

.no-image-big {
    font-size: clamp(70px, 8vw, 110px);
}


/* =========================================
   PRODUCT INFORMATION
========================================= */

.detail-info {
    flex: 1 1 50%;
    min-width: 280px;

    box-sizing: border-box;
}

.detail-info h2 {
    color: var(--green-dark);

    font-size: clamp(22px, 2.5vw, 32px);

    line-height: 1.3;

    margin: 0 0 8px;

    overflow-wrap: anywhere;
}

.detail-unit {
    color: var(--text-muted);

    margin-bottom: 14px;

    font-size: 14px;
}


/* =========================================
   PRICE
========================================= */

.detail-price {
    margin-bottom: 14px;

    display: flex;
    align-items: center;
    flex-wrap: wrap;

    gap: 6px;
}

.detail-price .old-price {
    text-decoration: line-through;

    color: #999;

    margin-right: 4px;

    font-size: 14px;
}

.discount-tag {
    background: var(--orange);
    color: #fff;

    padding: 3px 8px;

    border-radius: 4px;

    font-size: 12px;
    font-weight: 700;

    white-space: nowrap;
}

.detail-price .new-price {
    width: 100%;

    font-size: clamp(24px, 3vw, 32px);

    font-weight: 800;

    color: var(--green-dark);

    margin-top: 4px;
}


/* =========================================
   STOCK
========================================= */

.detail-stock {
    margin-bottom: 20px;

    font-weight: 600;

    line-height: 1.5;
}

.stock-in {
    color: var(--green);
}

.stock-out {
    color: #b3261e;
}


/* =========================================
   DESCRIPTION
========================================= */

.detail-desc {
    color: var(--text-muted);

    margin-bottom: 24px;

    line-height: 1.8;

    overflow-wrap: anywhere;
}


/* =========================================
   ADD TO CART
========================================= */

.add-cart-form {
    display: flex;
    align-items: center;

    gap: 12px;

    flex-wrap: wrap;
}

.add-cart-form label {
    font-weight: 600;
    white-space: nowrap;
}

.add-cart-form input[type="number"] {
    width: 70px;
    max-width: 100%;

    padding: 10px;

    border: 1px solid var(--border);
    border-radius: 6px;

    text-align: center;

    box-sizing: border-box;

    font-size: 15px;
}

.add-cart-form button {
    padding: 12px 26px;

    max-width: 100%;

    cursor: pointer;
}


/* =========================================
   RELATED PRODUCTS
========================================= */

.related-section {
    width: 100%;

    margin-bottom: 50px;
}


/* =========================================
   LARGE SCREENS / LED / 4K
========================================= */

@media (min-width: 1600px) {

    .product-detail {
        max-width: 1500px;

        gap: 50px;

        padding: 40px;
    }

    .detail-img {
        min-height: 430px;
    }

    .detail-img img {
        min-height: 430px;
    }

    .detail-info h2 {
        font-size: 34px;
    }

    .detail-desc {
        font-size: 17px;
    }

    .add-cart-form button {
        padding: 14px 30px;
        font-size: 16px;
    }
}


/* =========================================
   TABLET
   768px - 1199px
========================================= */

@media (min-width: 768px) and (max-width: 1199px) {

    .product-detail {
        gap: 25px;

        padding: 24px;
    }

    .detail-img {
        flex: 1 1 42%;
        min-width: 250px;
        min-height: 300px;
    }

    .detail-img img {
        min-height: 300px;
    }

    .detail-info {
        flex: 1 1 50%;
        min-width: 250px;
    }

    .detail-info h2 {
        font-size: 25px;
    }
}


/* =========================================
   MOBILE TABLET
   481px - 767px
========================================= */

@media (min-width: 481px) and (max-width: 767px) {

    .product-detail {
        width: 100%;

        flex-direction: column;

        gap: 22px;

        padding: 18px;

        margin-bottom: 35px;

        border-radius: 8px;
    }

    .detail-img {
        width: 100%;
        min-width: 0;

        min-height: 300px;

        flex: none;
    }

    .detail-img img {
        width: 100%;
        min-height: 300px;

        object-fit: cover;
    }

    .detail-info {
        width: 100%;
        min-width: 0;

        flex: none;
    }

    .detail-info h2 {
        font-size: 24px;
    }

    .detail-desc {
        font-size: 14px;
        line-height: 1.7;
    }

    .add-cart-form {
        width: 100%;
    }

    .add-cart-form button {
        flex: 1;
    }
}


/* =========================================
   SMALL MOBILE
   Up to 480px
========================================= */

@media (max-width: 480px) {

    .product-detail {
        width: 100%;

        display: flex;
        flex-direction: column;

        gap: 18px;

        padding: 12px;

        margin-bottom: 30px;

        border-radius: 8px;
    }


    /* ===== IMAGE ===== */

    .detail-img {
        width: 100%;

        min-width: 0;
        min-height: 240px;

        flex: none;

        border-radius: 8px;
    }

    .detail-img img {
        width: 100%;
        height: 240px;
        min-height: 240px;

        object-fit: cover;
    }

    .no-image-big {
        font-size: 65px;
    }


    /* ===== INFO ===== */

    .detail-info {
        width: 100%;

        min-width: 0;

        flex: none;
    }

    .detail-info h2 {
        font-size: 21px;

        line-height: 1.3;

        margin-bottom: 6px;
    }

    .detail-unit {
        font-size: 13px;

        margin-bottom: 12px;
    }


    /* ===== PRICE ===== */

    .detail-price {
        margin-bottom: 12px;

        gap: 5px;
    }

    .detail-price .old-price {
        font-size: 12px;
    }

    .discount-tag {
        font-size: 10px;

        padding: 3px 6px;
    }

    .detail-price .new-price {
        font-size: 24px;

        margin-top: 3px;
    }


    /* ===== STOCK ===== */

    .detail-stock {
        font-size: 13px;

        margin-bottom: 15px;
    }


    /* ===== DESCRIPTION ===== */

    .detail-desc {
        font-size: 13px;

        line-height: 1.65;

        margin-bottom: 18px;
    }


    /* ===== CART FORM ===== */

    .add-cart-form {
        width: 100%;

        display: grid;

        grid-template-columns: auto 75px;

        gap: 10px;

        align-items: center;
    }

    .add-cart-form label {
        font-size: 13px;
    }

    .add-cart-form input[type="number"] {
        width: 75px;

        padding: 9px 5px;

        font-size: 14px;
    }

    .add-cart-form button {
        width: 100%;

        grid-column: 1 / -1;

        padding: 11px 15px;

        font-size: 14px;
    }


    /* ===== RELATED ===== */

    .related-section {
        margin-bottom: 35px;
    }
}


/* =========================================
   VERY SMALL PHONES
   Up to 360px
========================================= */

@media (max-width: 360px) {

    .product-detail {
        padding: 10px;

        gap: 15px;
    }

    .detail-img {
        min-height: 210px;
    }

    .detail-img img {
        height: 210px;
        min-height: 210px;
    }

    .detail-info h2 {
        font-size: 19px;
    }

    .detail-price .new-price {
        font-size: 22px;
    }

    .detail-desc {
        font-size: 12px;
    }

    .add-cart-form {
        grid-template-columns: 1fr 65px;
    }

    .add-cart-form input[type="number"] {
        width: 65px;
    }

    .add-cart-form button {
        font-size: 13px;
        padding: 10px;
    }
}


/* =========================================
   PREVENT OVERFLOW
========================================= */

.product-detail,
.product-detail *,
.related-section,
.related-section * {
    box-sizing: border-box;
}

.product-detail img {
    max-width: 100%;
}
```