:root {
    --bg-gradient-start: #667eea;
    --bg-gradient-end: #764ba2;
    --bg-color: #f5f7fa;
    --card-bg: white;
    --text-color: #333;
    --text-secondary: #666;
    --heading-color: #667eea;
    --border-color: #e0e0e0;
    --input-bg: white;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --shadow-light: rgba(102, 126, 234, 0.4);
    --table-hover: #f8f9ff;
    --table-border: #f0f0f0;
    --success-color: #4caf50;
    --error-color: #ff4757;
    --error-bg: #ffe0e0;
    --error-text: #d32f2f;
    --info-bg: #e3f2fd;
    --info-text: #1976d2;
    --code-bg: #e0e0e0;

    /* Button Colors */
    --btn-bg: #667eea;
    --btn-text: white;
    --btn-hover: #5a67d8;
    --btn-logout-bg: #ff4757;
    --btn-logout-hover: #ff3838;

    /* Grade Colors */
    --grade-color: #4caf50;
    /* Green */
    --absent-color: #ff4757;
    /* Red */
    --empty-color: rgba(255, 71, 87, 0.5);
    /* Semi-transparent Red */
}

[data-theme="dark"] {
    --bg-gradient-start: #1a1c23;
    --bg-gradient-end: #2d3748;
    --bg-color: #1a202c;
    --card-bg: #2d3748;
    --text-color: #e2e8f0;
    --text-secondary: #a0aec0;
    --heading-color: #ffffff;
    /* White for better contrast */
    --border-color: #4a5568;
    --input-bg: #4a5568;
    --shadow-color: rgba(0, 0, 0, 0.5);
    --shadow-light: rgba(0, 0, 0, 0.3);
    --table-hover: #2c313d;
    --table-border: #4a5568;
    --success-color: #68d391;
    --error-color: #fc8181;
    --error-bg: #742a2a;
    --error-text: #feb2b2;
    --info-bg: #2c5282;
    --info-text: #bee3f8;
    --code-bg: #4a5568;

    /* Button Colors Dark Mode */
    --btn-bg: #5a67d8;
    /* Darker blue/indigo */
    --btn-text: white;
    --btn-hover: #4c51bf;
    --btn-logout-bg: #e53e3e;
    /* Darker red */
    --btn-logout-hover: #c53030;

    /* Grade Colors Dark Mode */
    --grade-color: #68d391;
    --absent-color: #fc8181;
    --empty-color: rgba(252, 129, 129, 0.5);
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    color: var(--text-color);
}

.container {
    width: 100%;
    max-width: 1200px;
}

.login-box,
.dashboard-box,
.grades-box {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 20px 60px var(--shadow-color);
    transition: background-color 0.3s, color 0.3s;
}

.login-box {
    max-width: 450px;
    margin: 0 auto;
}

h1 {
    color: var(--heading-color);
    text-align: center;
    margin-bottom: 10px;
    font-size: 2em;
}

h2 {
    color: var(--text-color);
    text-align: center;
    margin-bottom: 30px;
    font-size: 1.3em;
    font-weight: 500;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
    flex-wrap: wrap;
    gap: 15px;
}

.header h1 {
    margin: 0;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 15px;
}

.user-info span {
    color: var(--text-secondary);
}

.user-info strong {
    color: var(--text-color);
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    color: var(--text-color);
    font-weight: 500;
}

.form-group input {
    width: 100%;
    padding: 12px 15px;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    font-size: 16px;
    background-color: var(--input-bg);
    color: var(--text-color);
    transition: border-color 0.3s, background-color 0.3s;
}

.form-group input:focus {
    outline: none;
    border-color: var(--heading-color);
}

.btn-primary {
    width: 100%;
    padding: 14px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    border: none;
    border-radius: 10px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 20px var(--shadow-light);
}

.btn-logout {
    padding: 8px 20px;
    background: var(--btn-logout-bg);
    color: white;
    text-decoration: none;
    border-radius: 8px;
    font-size: 14px;
    transition: background 0.3s;
}

.btn-logout:hover {
    background: var(--btn-logout-hover);
}

.btn-back {
    display: inline-block;
    padding: 10px 20px;
    background: var(--btn-bg);
    color: var(--btn-text);
    text-decoration: none;
    border-radius: 8px;
    margin-bottom: 20px;
    transition: background 0.3s;
}

.btn-back:hover {
    background: var(--btn-hover);
}

.btn-sort {
    display: inline-block;
    padding: 10px 20px;
    background: var(--card-bg);
    color: var(--heading-color);
    text-decoration: none;
    border-radius: 8px;
    margin-bottom: 20px;
    margin-left: 10px;
    border: 2px solid var(--heading-color);
    transition: all 0.3s;
    font-weight: 600;
}

.btn-sort:hover {
    background: var(--heading-color);
    color: var(--card-bg);
}

.error-message {
    background: var(--error-bg);
    color: var(--error-text);
    padding: 15px;
    border-radius: 10px;
    margin-bottom: 20px;
    border-left: 4px solid var(--error-text);
}

.info-message {
    background: var(--info-bg);
    color: var(--info-text);
    padding: 15px;
    border-radius: 10px;
    margin-top: 20px;
    border-left: 4px solid var(--info-text);
}

.info-text {
    margin-top: 20px;
    padding: 15px;
    background: var(--bg-color);
    border-radius: 10px;
    text-align: center;
}

.info-text p {
    color: var(--text-secondary);
    font-size: 14px;
    line-height: 1.6;
}

.info-text code {
    background: var(--code-bg);
    padding: 2px 8px;
    border-radius: 4px;
    font-family: 'Courier New', monospace;
    color: var(--heading-color);
}

.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 20px;
    margin-top: 20px;
}

.subject-card {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 30px;
    border-radius: 15px;
    text-decoration: none;
    text-align: center;
    transition: transform 0.3s, box-shadow 0.3s;
    cursor: pointer;
}

.subject-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 15px 30px var(--shadow-light);
}

.subject-icon {
    font-size: 3em;
    margin-bottom: 15px;
}

.subject-name {
    font-size: 1.2em;
    font-weight: 600;
}

.grades-table-wrapper {
    overflow-x: auto;
    margin-top: 20px;
}

.grades-table {
    width: 100%;
    border-collapse: collapse;
    background: var(--card-bg);
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 5px 15px var(--shadow-color);
}

.grades-table thead {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.grades-table th {
    padding: 15px;
    text-align: left;
    font-weight: 600;
}

.grades-table td {
    padding: 15px;
    border-bottom: 1px solid var(--table-border);
    color: var(--text-color);
}

.grades-table tbody tr:hover {
    background: var(--table-hover);
}

.grades-table tbody tr:last-child td {
    border-bottom: none;
}

.grades-table td.grade-cell {
    font-weight: 600;
    font-size: 1.1em;
    color: var(--grade-color);
}

.grades-table td.grade-absent {
    color: var(--absent-color);
}

.grades-table td.grade-empty {
    color: var(--empty-color);
}

.navigation {
    margin-bottom: 20px;
}

/* Theme Toggle Button */
.theme-toggle {
    position: fixed;
    top: 20px;
    right: 20px;
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    border-radius: 50%;
    width: 45px;
    height: 45px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
    z-index: 1000;
    color: var(--text-color);
    font-size: 20px;
}

.theme-toggle:hover {
    transform: scale(1.1);
    border-color: var(--heading-color);
}

@media (max-width: 768px) {

    .login-box,
    .dashboard-box,
    .grades-box {
        padding: 25px;
    }

    h1 {
        font-size: 1.5em;
    }

    .header {
        flex-direction: column;
        align-items: flex-start;
    }

    .subjects-grid {
        grid-template-columns: 1fr;
    }

    .grades-table {
        font-size: 14px;
    }

    .grades-table th,
    .grades-table td {
        padding: 10px;
    }

    .theme-toggle {
        top: 10px;
        right: 10px;
        width: 40px;
        height: 40px;
        font-size: 18px;
    }
}

.row-green {
    background-color: rgba(76, 175, 80, 0.2) !important;
}

.row-red {
    background-color: rgba(255, 71, 87, 0.2) !important;
}