body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: #f4f7f6;
    color: #333;
    margin: 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}
.selection-page {
    align-items: center;
}
header {
    background-color: #2c3e50;
    color: white;
    padding: 1rem;
    text-align: center;
    width: 100%;
    box-sizing: border-box;
}
main {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 20px;
    width: 100%;
    box-sizing: border-box;
}
nav { margin-bottom: 20px; }
nav a { color: #3498db; text-decoration: none; font-weight: bold; }
.container {
    width: 100%;
    max-width: 600px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 15px;
    text-align: center;
    min-height: calc(100vh - 120px);
}
.card {
    background: white;
    padding: 20px;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    text-decoration: none;
    color: inherit;
    display: block;
    width: min(100%, 420px);
    transition: transform 0.2s;
    text-align: center;
}
.card:active { transform: scale(0.98); }
.qr-detail {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    height: 100vh; 
}
.qr-image {
    width: 80vw;
    max-width: 400px;
    height: auto;
    margin-bottom: 20px;
}
.btn-link {
    display: inline-block;
    background-color: #27ae60;
    color: white;
    padding: 15px 30px;
    border-radius: 50px;
    text-decoration: none;
    font-weight: bold;
    font-size: 1.2rem;
    box-shadow: 0 4px 15px rgba(39, 174, 96, 0.3);
}
.btn-back {
    position: absolute;
    top: 20px;
    left: 20px;
    color: #7f8c8d;
    text-decoration: none;
    font-size: 0.9rem;
}
h1 { margin-top: 0; }