.opp-container {
    max-width: 800px;
    margin: 2rem auto;
    padding: 20px;
    font-family: 'Poppins', sans-serif;
}

.opp-heading {
    text-align: center;
    color: #2c3e50;
    margin-bottom: 2rem;
    font-weight: 700;
}

.opp-upload-btn {
    display: block;
    width: 200px;
    margin: 20px auto;
    padding: 12px 24px;
    background: #3498db;
    color: white;
    border-radius: 5px;
    cursor: pointer;
    text-align: center;
    transition: background 0.3s;
}

.opp-upload-btn:hover {
    background: #2980b9;
}

.opp-preview-container {
    width: 500px;
    height: 500px;
    margin: 20px auto;
    border: 2px dashed #bdc3c7;
    position: relative;
}

#opp-preview-image {
    max-width: 100%;
    max-height: 100%;
}

.opp-controls {
    text-align: center;
    margin: 20px 0;
}

.opp-btn {
    padding: 12px 24px;
    background: #27ae60;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    margin: 0 10px;
    transition: background 0.3s;
}

.opp-btn:hover {
    background: #219a52;
}

#opp-a4-preview {
    margin: 20px auto;
    text-align: center;
}

#opp-a4-canvas {
    width: 100%;
    max-width: 794px; /* A4 width in pixels at 96 DPI */
    height: auto;
    border: 1px solid #ddd;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.opp-download-btns {
    margin: 20px 0;
}

.hidden {
    display: none;
}

@media (max-width: 768px) {
    .opp-preview-container {
        width: 90%;
        height: 300px;
    }
    
    .opp-btn {
        margin: 10px 0;
        width: 80%;
    }
}