* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Roboto', sans-serif;
}

:root {
    --primary-color: #6c5ce7;
    --primary-light: #a29bfe;
    --secondary-color: #2d3436;
    --text-color: #333;
    --light-gray: #f5f6fa;
    --success-color: #27ae60;
    --danger-color: #e74c3c;
    --warning-color: #f39c12;
    --info-color: #3498db;
    --border-radius: 8px;
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    --transition: all 0.3s ease;
}

body {
    background-color: #f9f9f9;
    color: var(--text-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    max-width: 900px;
    width: 100%;
    margin: 0 auto;
}

h1 {
    text-align: center;
    margin-bottom: 30px;
    color: var(--primary-color);
    font-weight: 700;
    font-size: 2.5rem;
}

h1 i {
    margin-right: 10px;
}

h2 {
    font-size: 1.5rem;
    color: var(--secondary-color);
    margin-bottom: 15px;
}

h2 i {
    margin-right: 8px;
}

.calculator {
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    overflow: hidden;
    margin-bottom: 30px;
}

/* Category tabs */
.category-tabs {
    display: flex;
    background-color: var(--secondary-color);
    overflow-x: auto;
    padding: 0 10px;
}

.category-btn {
    padding: 15px 20px;
    background: none;
    border: none;
    cursor: pointer;
    font-weight: 500;
    color: white;
    transition: var(--transition);
    white-space: nowrap;
    position: relative;
}

.category-btn i {
    margin-right: 8px;
    font-size: 1.1em;
}

.category-btn:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

.category-btn.active {
    color: var(--primary-light);
}

.category-btn.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 3px;
    background-color: var(--primary-light);
}

.calculator-content {
    position: relative;
}

.category-section {
    display: none;
}

.category-section.active {
    display: block;
    animation: fadeIn 0.5s;
}

/* Tab navigation within categories */
.tab-container {
    display: flex;
    background-color: var(--light-gray);
    border-bottom: 1px solid #ddd;
    overflow-x: auto;
}

.tab-btn {
    padding: 15px;
    background: none;
    border: none;
    cursor: pointer;
    font-weight: 500;
    color: var(--text-color);
    transition: var(--transition);
    white-space: nowrap;
    flex: 1;
    min-width: 150px;
}

.tab-btn i {
    margin-right: 6px;
    font-size: 0.9em;
}

.tab-btn:hover {
    background-color: rgba(108, 92, 231, 0.1);
}

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

.tab-content {
    padding: 25px;
}

.tab-pane {
    display: none;
}

.tab-pane.active {
    display: block;
    animation: fadeIn 0.5s;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.input-group {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 10px;
    margin-bottom: 20px;
}

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

.input-group label,
.input-group span {
    font-size: 1rem;
    color: var(--text-color);
}

.input-group label i {
    margin-right: 6px;
    color: var(--primary-color);
}

input[type="number"],
input[type="text"],
select {
    padding: 12px 15px;
    border: 1px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
    width: 100%;
    transition: var(--transition);
}

input[type="number"]:focus,
input[type="text"]:focus,
select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(108, 92, 231, 0.2);
}

.radio-group {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 15px;
    width: 100%;
}

.radio-group > div {
    display: flex;
    align-items: center;
    gap: 8px;
}

.radio-group label i {
    margin-right: 6px;
    color: var(--primary-color);
}

.calculate-btn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 12px 20px;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-weight: 500;
    transition: var(--transition);
    width: 100%;
    margin-bottom: 20px;
}

.calculate-btn i {
    margin-right: 8px;
}

.calculate-btn:hover {
    background-color: #5649c0;
    transform: translateY(-2px);
}

.result {
    background-color: var(--light-gray);
    padding: 15px;
    border-radius: var(--border-radius);
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
}

.result-group {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 15px;
}

.result-text {
    font-weight: 500;
}

.result-text i {
    margin-right: 6px;
    color: var(--primary-color);
}

.result-value {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--primary-color);
}

.formula {
    font-size: 0.85rem;
    color: #888;
    text-align: right;
    font-style: italic;
    margin-top: 10px;
}

.formula i {
    margin-right: 4px;
    color: #888;
}

.history-container {
    background-color: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 20px;
    margin-bottom: 30px;
}

.history-list {
    max-height: 200px;
    overflow-y: auto;
    margin-bottom: 15px;
}

.history-item {
    padding: 10px;
    border-bottom: 1px solid #eee;
    display: flex;
    justify-content: space-between;
}

.history-item:last-child {
    border-bottom: none;
}

.history-calculation {
    font-weight: 500;
}

.history-result {
    color: var(--primary-color);
}

.clear-btn {
    background-color: #e74c3c;
    color: white;
    border: none;
    padding: 10px 15px;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-weight: 500;
    transition: var(--transition);
}

.clear-btn i {
    margin-right: 6px;
}

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

.grade-info {
    background-color: var(--light-gray);
    padding: 15px;
    border-radius: var(--border-radius);
    margin-top: 15px;
    font-size: 0.9rem;
}

.grade-info p {
    margin-bottom: 5px;
}

.grade-info i {
    margin-right: 5px;
    color: var(--info-color);
}

.conversion-input {
    width: 100%;
    margin-top: 10px;
}

.increase {
    color: var(--success-color);
}

.decrease {
    color: var(--danger-color);
}

footer {
    margin-top: auto;
    text-align: center;
    padding: 20px;
    color: #888;
}

footer i.fa-heart {
    color: var(--danger-color);
    margin: 0 3px;
}

/* Responsive adjustments */
@media (max-width: 768px) {
    h1 {
        font-size: 2rem;
    }
    
    .category-btn {
        padding: 12px 10px;
        font-size: 0.9rem;
    }
    
    .category-btn i {
        margin-right: 5px;
    }
    
    .tab-btn {
        padding: 12px 8px;
        font-size: 0.9rem;
    }
    
    .tab-btn i {
        margin-right: 4px;
    }
    
    .tab-content {
        padding: 15px;
    }
    
    .input-group:not(.column) {
        flex-direction: column;
        align-items: flex-start;
    }
    
    input[type="number"],
    input[type="text"],
    select {
        width: 100%;
    }
}