:root {
    /* Default Dark Theme Variables */
    --bg-color: #121212;
    --container-bg: #1e1e1e;
    --text-color: #e0e0e0;
    --primary-color: #4a90e2;
    --secondary-text: #b0b0b0;
    --border-color: #333;
    --border-radius: 8px;

    /* Form Elements */
    --input-bg: #2c2c2c;
    --input-border: #444;
    --input-text: #fff;

    /* Alerts */
    --error-bg: #cf6679;
    --error-text: #fff;
    --success-bg: #03dac6;
    --success-text: #000;

    /* Interactive */
    --hover-bg: #333;
}

[data-theme="light"] {
    --bg-color: #f0f2f5;
    --container-bg: #ffffff;
    --text-color: #333333;
    --primary-color: #4a90e2;
    --secondary-text: #666666;
    --border-color: #ccc;

    /* Form Elements */
    --input-bg: #ffffff;
    --input-border: #ccc;
    --input-text: #333;

    /* Alerts */
    --error-bg: #f8d7da;
    --error-text: #721c24;
    --success-bg: #d4edda;
    --success-text: #155724;

    /* Interactive */
    --hover-bg: #f5f5f5;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    margin: 0;
    padding: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    background-color: var(--container-bg);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
    width: 100%;
    max-width: 600px;
    transition: background-color 0.3s, box-shadow 0.3s;
    position: relative;
}

header {
    text-align: center;
    margin-bottom: 2rem;
}

h1 {
    margin-bottom: 0.5rem;
    color: var(--primary-color);
}

.form-group {
    margin-bottom: 1.5rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: bold;
    color: var(--text-color);
}

/* File Upload */
input[type="file"] {
    display: none;
}

.custom-file-upload {
    border: 2px dashed var(--input-border);
    display: inline-block;
    padding: 12px 24px;
    cursor: pointer;
    border-radius: var(--border-radius);
    width: 100%;
    box-sizing: border-box;
    text-align: center;
    transition: border-color 0.3s, background-color 0.3s;
    background-color: var(--input-bg);
    color: var(--text-color);
}

.custom-file-upload:hover {
    border-color: var(--primary-color);
    background-color: var(--hover-bg);
}

#file-selected {
    display: block;
    margin-top: 0.5rem;
    font-style: italic;
    text-align: center;
    color: var(--secondary-text);
}

/* Checkboxes */
.checkbox-group {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
}

.checkbox-group label {
    font-weight: normal;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 12px 24px;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    text-decoration: none;
    transition: background-color 0.3s, transform 0.1s;
    width: 100%;
    box-sizing: border-box;
    text-align: center;
}

.btn:active {
    transform: scale(0.98);
}

.submit-btn {
    background-color: var(--primary-color);
    color: white;
}

.submit-btn:hover {
    filter: brightness(1.1);
}

.download-btn {
    background-color: #28a745;
    color: white;
}

.download-btn:hover {
    background-color: #218838;
}

/* Alerts */
.alert {
    padding: 1rem;
    border-radius: var(--border-radius);
    margin-bottom: 1rem;
    text-align: center;
}

.error {
    background-color: var(--error-bg);
    color: var(--error-text);
}

.success {
    background-color: var(--success-bg);
    color: var(--success-text);
}

.warning {
    background-color: #7a5c00;
    color: #ffe680;
    border: 1px solid #b38600;
}

.link {
    display: block;
    text-align: center;
    margin-top: 1rem;
    color: var(--primary-color);
    text-decoration: none;
}

.link:hover {
    text-decoration: underline;
}

.loader {
    text-align: center;
    font-weight: bold;
    color: var(--primary-color);
    margin-top: 1rem;
}

footer {
    text-align: center;
    margin-top: 2rem;
    font-size: 0.8rem;
    color: var(--secondary-text);
}

/* Theme Toggle Button */
.theme-toggle {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    cursor: pointer;
    color: var(--text-color);
    font-size: 1.5rem;
    padding: 0.5rem;
    border-radius: 50%;
    transition: background-color 0.3s;
    width: auto;
}

.theme-toggle:hover {
    background-color: var(--hover-bg);
}