```css
/* =====================================
   ULRICH OTAKU - DESIGN PRINCIPAL
===================================== */

:root {
    --background: #0B0B0F;
    --card: #151520;
    --purple: #9D4EDD;
    --red: #FF3040;
    --orange: #FF7A00;
    --white: #FFFFFF;
    --gray: #B8B8C7;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    scroll-padding-top: 90px;
}

body {
    background: var(--background);
    color: var(--white);
    font-family: Arial, Helvetica, sans-serif;
    line-height: 1.6;
}

button,
input {
    font: inherit;
}

button,
a {
    -webkit-tap-highlight-color: transparent;
}

a {
    color: inherit;
    text-decoration: none;
}

button {
    cursor: pointer;
}


/* =====================================
   EN-TÊTE
===================================== */

.header {
    width: 100%;
    min-height: 80px;
    padding: 18px 7%;
    background: rgba(11, 11, 15, 0.96);
    border-bottom: 1px solid rgba(157, 78, 221, 0.3);

    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 25px;

    position: sticky;
    top: 0;
    z-index: 1000;
}

.logo {
    font-size: 23px;
    font-weight: 900;
    letter-spacing: 1px;
    white-space: nowrap;
}

.logo span {
    color: var(--purple);
}

.navigation {
    display: flex;
    align-items: center;
    gap: 25px;
}

.navigation a {
    color: var(--gray);
    font-size: 14px;
    transition: color 0.3s;
}

.navigation a:hover {
    color: var(--purple);
}

.cart-button {
    padding: 10px 16px;
    border: 1px solid var(--purple);
    border-radius: 7px;
    background: transparent;
    color: var(--white);
    transition: 0.3s;
}

.cart-button:hover {
    background: var(--purple);
    box-shadow: 0 0 15px rgba(157, 78, 221, 0.5);
}


/* =====================================
   BANNIÈRE D'ACCUEIL
===================================== */

.hero {
    min-height: 540px;
    padding: 80px 8%;

    display: flex;
    align-items: center;

    background:
        radial-gradient(
            circle at 80% 40%,
            rgba(157, 78, 221, 0.25),
            transparent 35%
        ),
        radial-gradient(
            circle at 95% 90%,
            rgba(255, 48, 64, 0.18),
            transparent 30%
        ),
        linear-gradient(135deg, #0B0B0F, #171020);
    
    border-bottom: 1px solid rgba(157, 78, 221, 0.2);
}

.hero-content {
    max-width: 720px;
}

.hero-label,
.section-label {
    color: var(--orange);
    font-size: 13px;
    font-weight: bold;
    letter-spacing: 3px;
}

.hero h1 {
    margin: 20px 0;
    font-size: clamp(38px, 6vw, 72px);
    line-height: 1.12;
    font-weight: 900;
}

.hero h1 span {
    color: var(--purple);
    text-shadow: 0 0 25px rgba(157, 78, 221, 0.45);
}

.hero-description {
    max-width: 560px;
    margin-bottom: 32px;
    color: var(--gray);
    font-size: 17px;
}

.hero-button {
    display: inline-block;
    padding: 15px 24px;
    border-radius: 6px;
    background: linear-gradient(90deg, var(--purple), var(--red));
    color: var(--white);
    font-size: 13px;
    font-weight: bold;
    transition: transform 0.3s, box-shadow 0.3s;
}

.hero-button:hover {
    transform: translateY(-3px);
    box-shadow: 0 0 25px rgba(157, 78, 221, 0.4);
}


/* =====================================
   SECTIONS
===================================== */

.section {
    padding: 80px 7%;
}

.section-heading {
    margin-bottom: 35px;
    text-align: center;
}

.section-heading h2 {
    margin: 10px 0;
    font-size: clamp(28px, 4vw, 42px);
    font-weight: 900;
}

.section-heading h2 span {
    color: var(--purple);
}

.section-heading > p:last-child {
    color: var(--gray);
}


/* =====================================
   CATÉGORIES
===================================== */

.categories {
    background: #101016;
}

.category-list {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 14px;
}

.category-button {
    padding: 13px 20px;
    border: 1px solid #343044;
    border-radius: 8px;
    background: var(--card);
    color: var(--white);
    transition: 0.3s;
}

.category-button:hover,
.category-button.active {
    border-color: var(--purple);
    background: var(--purple);
    box-shadow: 0 0 15px rgba(157, 78, 221, 0.2);
}


/* =====================================
   RECHERCHE
===================================== */

.search-container {
    max-width: 650px;
    margin: 0 auto 40px;

    display: flex;
    gap: 10px;
}

.search-container input {
    width: 100%;
    min-width: 0;
    padding: 14px 16px;
    border: 1px solid #343044;
    border-radius: 7px;
    outline: none;
    background: var(--card);
    color: var(--white);
}

.search-container input:focus {
    border-color: var(--purple);
}

.search-container button {
    padding: 14px 18px;
    border: none;
    border-radius: 7px;
    background: var(--purple);
    color: var(--white);
    font-weight: bold;
    transition: 0.3s;
}

.search-container button:hover {
    background: var(--red);
}


/* =====================================
   CARTES DES PRODUITS
===================================== */

.product-grid {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 24px;
}

.product-card {
    overflow: hidden;
    border: 1px solid #282535;
    border-radius: 12px;
    background: var(--card);
    transition: transform 0.3s, border-color 0.3s;
}

.product-card:hover {
    transform: translateY(-6px);
    border-color: var(--purple);
}

.product-image {
    width: 100%;
    height: 220px;
    object-fit: cover;
    display: block;
    background: #22202D;
}

.product-info {
    padding: 18px;
}

.product-category {
    color: var(--orange);
    font-size: 11px;
    font-weight: bold;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.product-info h3 {
    margin: 8px 0;
    font-size: 17px;
}

.product-description {
    min-height: 44px;
    margin-bottom: 12px;
    color: var(--gray);
    font-size: 13px;
}

.product-price {
    margin-bottom: 15px;
    color: var(--purple);
    font-size: 19px;
    font-weight: 900;
}

.add-to-cart {
    width: 100%;
    padding: 12px;
    border: none;
    border-radius: 6px;
    background: linear-gradient(90deg, var(--purple), #7038B4);
    color: var(--white);
    font-weight: bold;
    transition: 0.3s;
}

.add-to-cart:hover {
    background: linear-gradient(90deg, var(--red), var(--orange));
}

.empty-message {
    padding: 30px;
    color: var(--gray);
    text-align: center;
}


/* =====================================
   PANIER
===================================== */

.cart-section {
    background: #101016;
}

#cart-items {
    max-width: 850px;
    margin: 0 auto;
}

.cart-empty {
    padding: 30px;
    border: 1px dashed #343044;
    border-radius: 8px;
    color: var(--gray);
    text-align: center;
}

.cart-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 15px;

    margin-bottom: 12px;
    padding: 18px;

    border: 1px solid #282535;
    border-radius: 8px;
    background: var(--card);
}

.cart-item h3 {
    font-size: 15px;
}

.cart-item p {
    color: var(--purple);
    font-weight: bold;
}

.cart-actions {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 8px;
}

.quantity-button,
.remove-button {
    padding: 7px 11px;
    border: 1px solid #454052;
    border-radius: 5px;
    background: transparent;
    color: var(--white);
}

.quantity-button:hover {
    border-color: var(--purple);
    background: var(--purple);
}

.remove-button {
    border-color: var(--red);
    color: #FF6570;
}

.remove-button:hover {
    background: var(--red);
    color: var(--white);
}

.cart-summary {
    max-width: 850px;
    margin: 30px auto 0;
    padding: 24px;
    border: 1px solid #343044;
    border-radius: 10px;
    background: var(--card);
}

.cart-summary h3 {
    margin-bottom: 20px;
    font-size: 22px;
}

#cart-total {
    color: var(--purple);
}

.checkout-button {
    width: 100%;
    padding: 14px;
    border: none;
    border-radius: 6px;
    background: linear-gradient(90deg, var(--red), var(--orange));
    color: var(--white);
    font-weight: bold;
}

.checkout-button:disabled {
    cursor: not-allowed;
    opacity: 0.45;
}

.cart-notice {
    margin-top: 12px;
    color: var(--gray);
    font-size: 12px;
    text-align: center;
}


/* =====================================
   PIED DE PAGE
===================================== */

.footer {
    padding: 40px 7%;
    border-top: 1px solid rgba(157, 78, 221, 0.3);
    text-align: center;
}

.footer > p {
    margin-top: 12px;
    color: var(--gray);
}

.copyright {
    font-size: 12px;
}


/* =====================================
   ADAPTATION AUX TABLETTES
===================================== */

@media (max-width: 1050px) {
    .header {
        flex-wrap: wrap;
    }

    .navigation {
        gap: 15px;
    }

    .product-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}


/* =====================================
   ADAPTATION AUX TÉLÉPHONES
===================================== */

@media (max-width: 650px) {
    .header {
        justify-content: center;
        padding: 16px 5%;
    }

    .logo {
        font-size: 21px;
    }

    .navigation {
        width: 100%;
        justify-content: center;
        flex-wrap: wrap;
        gap: 12px;
    }

    .navigation a {
        font-size: 12px;
    }

    .cart-button {
        padding: 8px 12px;
    }

    .hero {
        min-height: 450px;
        padding: 60px 6%;
    }

    .hero-description {
        font-size: 15px;
    }

    .section {
        padding: 55px 5%;
    }

    .product-grid {
        grid-template-columns: 1fr;
    }

    .product-image {
        height: 250px;
    }

    .search-container {
        flex-direction: column;
    }

    .cart-item {
        align-items: flex-start;
        flex-direction: column;
    }

    .cart-actions {
        width: 100%;
    }
}
```