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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: #f5f5f5;
    color: #333;
    line-height: 1.6;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 2rem;
    background-color: white;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    margin-top: 2rem;
}

h1 {
    text-align: center;
    color: #2c3e50;
    margin-bottom: 2rem;
}

h3 {
    color: #34495e;
    margin-bottom: 1rem;
}

.upload-section,
.column-section,
.lowercase-section,
.regex-section {
    margin-bottom: 2rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: #555;
}

input[type="file"],
input[type="text"],
select {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: 5px;
    font-size: 1rem;
    transition: border-color 0.3s;
}

.lowercase-section label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
}

input[type="checkbox"] {
    width: 1.2rem;
    height: 1.2rem;
    cursor: pointer;
}

input[type="file"]:hover,
input[type="text"]:focus,
select:focus,
input[type="checkbox"]:focus {
    border-color: #3498db;
    outline: none;
}

.regex-input {
    margin-bottom: 1rem;
    padding: 1rem;
    background-color: #f8f9fa;
    border-radius: 5px;
}

.regex-input input[type="text"] {
    margin-bottom: 0.5rem;
}

.regex-input input[type="text"]:last-child {
    margin-bottom: 0;
}

button {
    background-color: #3498db;
    color: white;
    padding: 0.75rem 2rem;
    border: none;
    border-radius: 5px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.3s;
    display: block;
    margin: 0 auto;
}

button:hover:not(:disabled) {
    background-color: #2980b9;
}

button:disabled {
    background-color: #bdc3c7;
    cursor: not-allowed;
}

#downloadBtn {
    background-color: #27ae60;
    margin-top: 1rem;
}

#downloadBtn:hover {
    background-color: #229954;
}

.preview-section {
    margin-top: 2rem;
    padding: 1rem;
    background-color: #f8f9fa;
    border-radius: 5px;
    max-height: 400px;
    overflow-y: auto;
}

.preview-section table {
    width: 100%;
    border-collapse: collapse;
}

.preview-section th,
.preview-section td {
    padding: 0.5rem;
    text-align: left;
    border-bottom: 1px solid #ddd;
}

.preview-section th {
    background-color: #34495e;
    color: white;
    position: sticky;
    top: 0;
}

.preview-section tr:hover {
    background-color: #e8e8e8;
}

.modified {
    background-color: #fff3cd;
    font-weight: 600;
}

.status {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: 5px;
    text-align: center;
    font-weight: 600;
}

.status.success {
    background-color: #d4edda;
    color: #155724;
    border: 1px solid #c3e6cb;
}

.status.error {
    background-color: #f8d7da;
    color: #721c24;
    border: 1px solid #f5c6cb;
}

.status.info {
    background-color: #d1ecf1;
    color: #0c5460;
    border: 1px solid #bee5eb;
}

@media (max-width: 600px) {
    .container {
        margin: 1rem;
        padding: 1rem;
    }
    
    button {
        width: 100%;
    }
}