```css
/* =========================================
   STYLE GLOBAL - VENTE DE LOGICIELS
========================================= */

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background: #f5f7fa;
    color: #1f2937;
    line-height: 1.6;
}

/* =========================================
   LIENS
========================================= */

a {
    color: #2563eb;
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

/* =========================================
   HEADER
========================================= */

header {
    background: #111827;
    color: white;
    padding: 18px 40px;

    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 20px;
}

header h1 {
    font-size: 24px;
}

nav {
    display: flex;
    align-items: center;
    gap: 20px;
}

nav a {
    color: white;
    font-weight: 500;
}

nav a:hover {
    color: #60a5fa;
    text-decoration: none;
}

/* =========================================
   CONTENU PRINCIPAL
========================================= */

main {
    width: 90%;
    max-width: 1200px;
    margin: 40px auto;
}

section {
    margin-bottom: 30px;
}

h1,
h2,
h3 {
    margin-bottom: 15px;
}

/* =========================================
   CARTES LOGICIELS
========================================= */

article {
    background: white;
    border-radius: 10px;
    padding: 25px;
    margin-bottom: 20px;

    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
}

article img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    margin-bottom: 15px;
}

/* =========================================
   BOUTONS
========================================= */

button,
.btn {
    display: inline-block;

    border: none;
    border-radius: 6px;

    background: #2563eb;
    color: white;

    padding: 11px 18px;

    font-size: 15px;
    font-weight: 600;

    cursor: pointer;

    text-decoration: none;
}

button:hover,
.btn:hover {
    background: #1d4ed8;
    text-decoration: none;
}

/* Bouton secondaire */

.btn-secondary {
    background: #6b7280;
}

.btn-secondary:hover {
    background: #4b5563;
}

/* Bouton danger */

.btn-danger {
    background: #dc2626;
}

.btn-danger:hover {
    background: #b91c1c;
}

/* Bouton succès */

.btn-success {
    background: #16a34a;
}

.btn-success:hover {
    background: #15803d;
}

/* =========================================
   FORMULAIRES
========================================= */

form {
    background: white;
    padding: 30px;

    border-radius: 10px;

    max-width: 600px;

    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
}

label {
    display: block;

    margin-bottom: 7px;

    font-weight: 600;
}

input,
select,
textarea {
    width: 100%;

    padding: 11px 13px;

    border: 1px solid #d1d5db;

    border-radius: 6px;

    font-size: 15px;

    background: white;
}

input:focus,
select:focus,
textarea:focus {
    outline: none;

    border-color: #2563eb;

    box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.12);
}

textarea {
    min-height: 120px;
    resize: vertical;
}

/* =========================================
   MESSAGES
========================================= */

.message {
    padding: 14px 18px;

    border-radius: 6px;

    margin-bottom: 20px;
}

.message-error {
    background: #fee2e2;
    color: #991b1b;
}

.message-success {
    background: #dcfce7;
    color: #166534;
}

.message-info {
    background: #dbeafe;
    color: #1e40af;
}

/* =========================================
   TABLEAUX
========================================= */

table {
    width: 100%;

    border-collapse: collapse;

    background: white;

    margin-top: 20px;
}

th,
td {
    padding: 13px 15px;

    border-bottom: 1px solid #e5e7eb;

    text-align: left;
}

th {
    background: #111827;
    color: white;
}

tr:hover {
    background: #f9fafb;
}

/* =========================================
   PRIX
========================================= */

.prix {
    font-size: 22px;

    font-weight: bold;

    color: #16a34a;

    margin: 15px 0;
}

/* =========================================
   BADGES
========================================= */

.badge {
    display: inline-block;

    padding: 5px 10px;

    border-radius: 20px;

    font-size: 13px;

    font-weight: 600;
}

.badge-success {
    background: #dcfce7;
    color: #166534;
}

.badge-warning {
    background: #fef3c7;
    color: #92400e;
}

.badge-danger {
    background: #fee2e2;
    color: #991b1b;
}

.badge-info {
    background: #dbeafe;
    color: #1e40af;
}

/* =========================================
   FOOTER
========================================= */

footer {
    background: #111827;

    color: white;

    text-align: center;

    padding: 25px;

    margin-top: 60px;
}

/* =========================================
   UTILITAIRES
========================================= */

.text-center {
    text-align: center;
}

.mt-20 {
    margin-top: 20px;
}

.mb-20 {
    margin-bottom: 20px;
}

.flex {
    display: flex;
}

.flex-between {
    display: flex;

    justify-content: space-between;

    align-items: center;

    gap: 20px;
}

/* =========================================
   RESPONSIVE
========================================= */

@media (max-width: 768px) {

    header {
        padding: 15px 20px;

        flex-direction: column;

        align-items: flex-start;
    }

    nav {
        flex-wrap: wrap;

        gap: 12px;
    }

    main {
        width: 94%;

        margin: 25px auto;
    }

    table {
        display: block;

        overflow-x: auto;

        white-space: nowrap;
    }

    form {
        padding: 20px;
    }

}
```