:root {
    --bg-color: #f0f2f5;
    --container-bg: white;
    --text-color: #333;
}

body.dark-mode {
    --bg-color: #121212;
    --container-bg: #1e1e1e;
    --text-color: #ffffff;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    background-image: url("data:image/svg+xml,%3csvg width='100' height='100' viewBox='0 0 100 100' xmlns='http://www.w3.org/2000/svg'%3e%3cfilter id='noise' x='0' y='0'%3e%3cfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3e%3c/filter%3e%3crect width='100%25' height='100%25' filter='url(%23noise)' opacity='0.05'/%3e%3c/svg%3e");
    transition: background-color 0.3s, color 0.3s;
}

.container {
    text-align: center;
    background-color: var(--container-bg);
    padding: 40px;
    border-radius: 16px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    transition: background-color 0.3s;
    position: relative;
    max-width: 500px;
    width: 90%;
    max-height: 90vh;
    overflow-y: auto;
}

h1 {
    font-size: 2.5em;
    color: var(--text-color);
    margin-bottom: 30px;
}

.theme-toggle-btn {
    position: absolute;
    top: 20px;
    right: 20px;
    background: none;
    border: none;
    font-size: 1.5em;
    cursor: pointer;
    color: var(--text-color);
    transition: transform 0.2s;
}

.theme-toggle-btn:hover {
    transform: scale(1.1);
}

.spinner {
    border: 4px solid rgba(0, 0, 0, 0.1);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border-left-color: #007bff;
    animation: spin 1s linear infinite;
    margin: 0 auto 10px auto;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

body.dark-mode .spinner {
    border: 4px solid rgba(255, 255, 255, 0.1);
    border-left-color: #007bff;
}

.upload-btn {
    display: inline-block;
    background-color: #28a745;
    color: white;
    padding: 12px 24px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.1em;
    font-weight: bold;
    transition: background-color 0.3s, box-shadow 0.3s;
    box-shadow: 0 4px 15px rgba(40, 167, 69, 0.3);
}

.upload-btn:hover {
    background-color: #218838;
    box-shadow: 0 6px 20px rgba(40, 167, 69, 0.4);
}

.nav-link {
    display: inline-block;
    padding: 10px 20px;
    background-color: var(--text-color);
    color: var(--container-bg);
    text-decoration: none;
    border-radius: 8px;
    transition: opacity 0.3s;
    font-weight: bold;
}

.nav-link:hover {
    opacity: 0.8;
}