:root {
    --primary-color: #083757;
    --secondary-color: #2ecc71;
    --danger-color: #e74c3c;
    --warning-color: #f39c12;
    --dark-color: #2c3e50;
    --light-color: #ecf0f1;
    --gray-color: #95a5a6;
    --white-color: #ffffff;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --border-radius: 8px;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f5f7fa;
}

header {
    background-color: var(--primary-color);
    color: var(--white-color);
    padding: 1.5rem 0;
    text-align: center;
    margin-bottom: 2rem;
}

header h1 {
    font-size: 2.2rem;
    margin-bottom: 0.5rem;
}

header p {
    font-size: 1.1rem;
    opacity: 0.9;
}

main {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 20px;
}

.tabs {
    display: flex;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid #ddd;
}

.tab-btn {
    padding: 0.8rem 1.5rem;
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 600;
    color: var(--gray-color);
    border-bottom: 3px solid transparent;
    transition: all 0.3s ease;
}

.tab-btn:hover {
    color: var(--primary-color);
}

.tab-btn.active {
    color: var(--primary-color);
    border-bottom: 3px solid var(--primary-color);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

.container {
    background-color: var(--white-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 1.5rem;
    margin-bottom: 2rem;
}

.container h2 {
    color: var(--dark-color);
    margin-bottom: 1.5rem;
    font-size: 1.5rem;
}

.container h2 i {
    margin-right: 0.5rem;
    color: var(--primary-color);
}

.form-group {
    margin-bottom: 1.2rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--dark-color);
}

label i {
    margin-right: 0.5rem;
    color: var(--primary-color);
}

input, select {
    width: 100%;
    padding: 0.8rem;
    border: 1px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: border 0.3s;
}

input:focus, select:focus {
    outline: none;
    border-color: var(--primary-color);
}

.button-group {
    display: flex;
    gap: 1rem;
    margin: 1.5rem 0;
    flex-wrap: wrap;
}

.btn {
    padding: 0.8rem 1.5rem;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    font-weight: 600;
    transition: all 0.3s;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.btn i {
    font-size: 1rem;
}

.add-btn {
    background-color: var(--secondary-color);
    color: var(--white-color);
}

.add-btn:hover {
    background-color: #27ae60;
}

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

.calculate-btn:hover {
    background-color: #2980b9;
}

.save-btn {
    background-color: var(--warning-color);
    color: var(--white-color);
}

.save-btn:hover {
    background-color: #d35400;
}

#course-entries {
    margin-bottom: 1.5rem;
}

.course-row {
    display: flex;
    gap: 1rem;
    margin-bottom: 1rem;
    align-items: center;
}

.course-row input, .course-row select {
    flex: 1;
    min-width: 0;
}

.remove-btn {
    background-color: var(--danger-color);
    color: var(--white-color);
    padding: 0.8rem;
    width: auto;
    min-width: 40px;
}

.remove-btn:hover {
    background-color: #c0392b;
}

.result-box {
    background-color: #e8f4fc;
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-top: 1.5rem;
    display: none;
}

.result-box h3 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.2rem;
}

.result-content {
    font-size: 1.1rem;
    line-height: 1.8;
}

.result-content strong {
    color: var(--dark-color);
    font-size: 1.3rem;
}

.grade-scale-table {
    overflow-x: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 1rem;
}

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

th {
    background-color: var(--primary-color);
    color: var(--white-color);
    font-weight: 600;
}

tr:nth-child(even) {
    background-color: #f8f9fa;
}

.history-actions {
    margin-bottom: 1.5rem;
}

.history-item {
    background-color: #f8f9fa;
    border-radius: var(--border-radius);
    padding: 1rem;
    margin-bottom: 1rem;
    border-left: 4px solid var(--primary-color);
}

.history-item h3 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.history-item p {
    color: var(--dark-color);
    margin-bottom: 0.5rem;
}

.history-item .history-date {
    color: var(--gray-color);
    font-size: 0.9rem;
}

footer {
    text-align: center;
    padding: 1.5rem;
    color: var(--gray-color);
    font-size: 0.9rem;
    margin-top: 2rem;
}

@media (max-width: 768px) {
    .tabs {
        flex-wrap: wrap;
    }
    
    .tab-btn {
        flex: 1 0 auto;
        padding: 0.8rem;
        font-size: 0.9rem;
    }
    
    .course-row {
        flex-direction: column;
        gap: 0.8rem;
    }
    
    .button-group {
        flex-direction: column;
    }
    
    .btn {
        width: 100%;
    }
}