body {
    font-family: 'Comic Sans MS', 'Trebuchet MS', Arial, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    margin: 0;
    color: #333;
    min-height: 100vh;
}

body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 50%;
    height: 50%;
    background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><circle cx="20" cy="20" r="2" fill="%23ffffff" opacity="0.1"/><circle cx="80" cy="40" r="3" fill="%23ffeb3b" opacity="0.1"/><circle cx="40" cy="70" r="2" fill="%23ff9800" opacity="0.1"/><circle cx="70" cy="10" r="1" fill="%23e91e63" opacity="0.1"/><circle cx="10" cy="60" r="2" fill="%234caf50" opacity="0.1"/></svg>') repeat;
    z-index: -1;
    pointer-events: none;
}

header {
    background: linear-gradient(45deg, #ff6b6b, #4ecdc4, #45b7d1, #96ceb4);
    background-size: 200% 200%;
    animation: gradientShift 8s ease infinite;
    color: #fff;
    padding: 1rem 0.5rem;
    text-align: center;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: 0 4px 20px rgba(0,0,0,0.15);
    position: relative;
}

/* Decorative logo watermark behind header title */
header::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 120px;
    height: 120px;
    /* Replace 'default-logo.png' with your actual logo image */
    background: url('default-logo.png') no-repeat center center;
    background-size: contain;
    opacity: 0.15;
    z-index: 1;
    pointer-events: none;
}

@keyframes gradientShift {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}

header h1 {
    font-size: 1.8rem;
    margin: 0 0 0.25rem 0;
    letter-spacing: 0.5px;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
    font-weight: 700;
    position: relative;
    z-index: 2;
}

header p {
    font-size: 0.95rem;
    margin: 0;
    opacity: 0.95;
    text-shadow: 1px 1px 2px rgba(0,0,0,0.2);
    position: relative;
    z-index: 2;
}

.grades {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 2.5rem;
    padding: 3rem 1rem;
}

.main-container {
    display: grid;
    grid-template-columns: 280px 1fr;
    gap: 2.5rem;
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

.left-sidebar {
    background: linear-gradient(145deg, #ffffff, #f0f8ff);
    border-radius: 1.5rem;
    padding: 2rem;
    box-shadow: 0 6px 25px rgba(31, 38, 135, 0.2);
    border: 1px solid rgba(255, 255, 255, 0.3);
    height: fit-content;
    position: sticky;
    top: 120px;
}

.left-sidebar h3 {
    color: #2d3748;
    font-size: 1.4rem;
    margin-bottom: 1.2rem;
    font-weight: 700;
    text-align: center;
}

.left-sidebar p {
    color: #4a5568;
    font-size: 1rem;
    line-height: 1.7;
    margin-bottom: 1.2rem;
    text-align: left;
}

.left-sidebar .highlight {
    background: linear-gradient(120deg, #a8edea 0%, #fed6e3 100%);
    padding: 1rem;
    border-radius: 1rem;
    margin: 1.2rem 0;
    border-left: 4px solid #4ecdc4;
}

.left-sidebar .highlight p {
    margin: 0;
    font-weight: 600;
    color: #2d3748;
}

.left-sidebar ul {
    font-size: 0.95rem;
    color: #4a5568;
    line-height: 1.6;
    margin: 1rem 0;
    padding-left: 1.2rem;
}

.content-area {
    min-width: 0;
}

.grade-card {
    background: linear-gradient(145deg, #ffffff, #f8f9fa);
    border-radius: 2rem;
    box-shadow: 0 8px 32px rgba(31, 38, 135, 0.37);
    backdrop-filter: blur(4px);
    border: 1px solid rgba(255, 255, 255, 0.18);
    width: 340px;
    max-width: 90vw;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    margin-bottom: 1rem;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    position: relative;
    overflow: hidden;
}

.grade-card:hover {
    transform: translateY(-8px);
    box-shadow: 0 12px 40px rgba(31, 38, 135, 0.5);
}

.grade-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 6px;
    background: linear-gradient(45deg, #ff6b6b, #4ecdc4, #45b7d1, #96ceb4);
    background-size: 400% 400%;
    animation: gradientShift 6s ease infinite;
}

.grade-title {
    font-size: 1.6rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    color: #2d3748;
    text-shadow: 1px 1px 2px rgba(0,0,0,0.1);
}

.grade-age {
    font-size: 1.1rem;
    margin-bottom: 1.5rem;
    color: #4a5568;
    font-weight: 500;
}

.product-image {
    width: 150px;
    height: 150px;
    object-fit: cover;
    border-radius: 1rem;
    margin-bottom: 1rem;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

.product-title {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: #2d3748;
    line-height: 1.4;
}

.buy-btn {
    background: linear-gradient(45deg, #ff6b6b, #ee5a24);
    color: #fff;
    border: none;
    border-radius: 1.5rem;
    padding: 1rem 2.5rem;
    font-size: 1.1rem;
    font-weight: 700;
    text-decoration: none;
    margin-bottom: 0.5rem;
    transition: all 0.3s;
    cursor: pointer;
    box-shadow: 0 4px 15px rgba(255, 107, 107, 0.4);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.buy-btn:hover {
    background: linear-gradient(45deg, #ee5a24, #ff6b6b);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(255, 107, 107, 0.6);
}

/* Backpack Section Styling */
.backpack-card {
    border: 2px solid #4ecdc4;
    background: linear-gradient(145deg, #f0ffff, #ffffff);
}

.backpack-card::before {
    background: linear-gradient(45deg, #4ecdc4, #45b7d1, #96ceb4, #ff6b6b);
    height: 8px;
}

.backpack-card .grade-title {
    color: #2c5aa0;
    font-size: 1.7rem;
}

.backpack-card .grade-age {
    color: #4ecdc4;
    font-weight: 600;
}

.backpack-card .buy-btn {
    background: linear-gradient(45deg, #4ecdc4, #45b7d1);
    box-shadow: 0 4px 15px rgba(78, 205, 196, 0.4);
}

.backpack-card .buy-btn:hover {
    background: linear-gradient(45deg, #45b7d1, #4ecdc4);
    box-shadow: 0 6px 20px rgba(78, 205, 196, 0.6);
}

footer {
    background: linear-gradient(45deg, #2d3748, #4a5568);
    color: #fff;
    text-align: center;
    padding: 3rem 1rem;
    font-size: 1.1rem;
    margin-top: 3rem;
}

.footer-tips {
    font-size: 1.3rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: #ffd700;
}

.footer-message {
    font-size: 1.1rem;
    margin-bottom: 1rem;
    font-style: italic;
}

.footer-copyright {
    font-size: 0.9rem;
    opacity: 0.8;
}

/* Responsive Design */
@media (max-width: 1200px) {
    .main-container {
        grid-template-columns: 250px 1fr;
        gap: 2rem;
    }
    .left-sidebar {
        padding: 1.5rem;
    }
}

@media (max-width: 900px) {
    .main-container {
        grid-template-columns: 1fr;
        gap: 2rem;
        padding: 1rem;
    }
    .left-sidebar {
        order: 1;
        position: static;
        margin-bottom: 2rem;
        text-align: center;
    }
    .content-area {
        order: 2;
    }
}

@media (max-width: 700px) {
    .grades {
        flex-direction: column;
        align-items: center;
        gap: 2rem;
        padding: 2rem 1rem;
    }
    .grade-card {
        width: 95vw;
        max-width: 99vw;
        padding: 1.5rem;
    }
    header::before {
        width: 100px;
        height: 100px;
        opacity: 0.1;
    }
    header h1 {
        font-size: 1.5rem;
    }
    header p {
        font-size: 0.85rem;
    }
}