/* ========================================
   CSS VARIABLES & DESIGN TOKENS
   ======================================== */
:root {
    /* Colors - Dark Theme */
    --bg-primary: #1a1a1a;
    --bg-secondary: #2a2a2a;
    --bg-tertiary: #1e1e1e;
    --border-color: #444444;
    --text-primary: #ffffff;
    --text-secondary: #888888;
    --text-tertiary: #666666;
    
    /* Accent Colors */
    --accent-orange: #FF9800;
    --accent-orange-dark: #F57C00;
    --accent-blue: #2196F3;
    --accent-green: #4CAF50;
    --accent-red: #F44336;
    --accent-purple: #9C27B0;
    
    /* Gradients */
    --gradient-orange: linear-gradient(135deg, #FF9800, #F57C00);
    --gradient-blue: linear-gradient(135deg, rgba(33, 150, 243, 0.1), #2a2a2a);
    --gradient-green: linear-gradient(135deg, rgba(76, 175, 80, 0.1), #2a2a2a);
    
    /* Shadows */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 8px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 8px 16px rgba(0, 0, 0, 0.4);
    --shadow-orange: 0 4px 12px rgba(255, 152, 0, 0.3);
    --shadow-blue: 0 4px 12px rgba(33, 150, 243, 0.3);
    --shadow-green: 0 4px 12px rgba(76, 175, 80, 0.3);
    
    /* Spacing */
    --space-xs: 8px;
    --space-sm: 12px;
    --space-md: 16px;
    --space-lg: 24px;
    --space-xl: 32px;
    
    /* Border Radius */
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    --radius-pill: 20px;
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-base: 0.3s ease;
    --transition-slow: 0.5s ease;
    
    /* Typography */
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
}

/* Light Theme */
body.light-theme {
    --bg-primary: #f5f5f5;
    --bg-secondary: #ffffff;
    --bg-tertiary: #fafafa;
    --border-color: #e0e0e0;
    --text-primary: #1a1a1a;
    --text-secondary: #666666;
    --text-tertiary: #888888;
}

/* ========================================
   RESET & BASE STYLES
   ======================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    transition: background-color var(--transition-base), color var(--transition-base);
}

/* ========================================
   HEADER
   ======================================== */
.app-header {
    background-color: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-md);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-md) var(--space-lg);
    max-width: 1200px;
    margin: 0 auto;
}

.header-left {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.app-logo {
    display: flex;
    align-items: center;
    justify-content: center;
}

.app-title {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

.header-right {
    display: flex;
    gap: var(--space-sm);
    position: relative;
}

.icon-btn {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    width: 40px;
    height: 40px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.icon-btn:hover {
    background-color: var(--bg-tertiary);
    border-color: var(--accent-orange);
    transform: translateY(-2px);
}

.theme-icon {
    transition: opacity var(--transition-fast);
}

body.light-theme .sun-icon {
    display: none;
}

body:not(.light-theme) .moon-icon {
    display: none;
}

/* Menu Dropdown */
.menu-dropdown {
    position: absolute;
    top: calc(100% + 8px);
    right: 0;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    min-width: 200px;
    box-shadow: var(--shadow-lg);
    overflow: hidden;
    opacity: 1;
    transform: translateY(0);
    transition: all var(--transition-fast);
}

.menu-dropdown.hidden {
    opacity: 0;
    transform: translateY(-10px);
    pointer-events: none;
}

.menu-item {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-md);
    width: 100%;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-size: 0.95rem;
    cursor: pointer;
    transition: background-color var(--transition-fast);
    text-align: left;
}

.menu-item:hover {
    background-color: var(--bg-tertiary);
}

.menu-item:not(:last-child) {
    border-bottom: 1px solid var(--border-color);
}

/* Tabs */
.tabs {
    display: flex;
    max-width: 1200px;
    margin: 0 auto;
    border-top: 1px solid var(--border-color);
}

.tab {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-xs);
    padding: var(--space-md);
    background: transparent;
    border: none;
    border-bottom: 3px solid transparent;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.tab:hover {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

.tab.active {
    color: var(--accent-orange);
    border-bottom-color: var(--accent-orange);
}

/* ========================================
   MAIN CONTENT
   ======================================== */
.main-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--space-lg);
}

.container {
    max-width: 800px;
    margin: 0 auto;
}

.tab-content {
    display: none;
    animation: fadeIn var(--transition-base);
}

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

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

/* ========================================
   CALCULATE TAB
   ======================================== */
.input-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
}

.input-card {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--space-md);
    transition: all var(--transition-fast);
}

.input-card:hover {
    border-color: var(--accent-orange);
    box-shadow: var(--shadow-sm);
}

.input-card label {
    display: block;
    color: var(--text-secondary);
    font-size: 0.75rem;
    margin-bottom: var(--space-xs);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.input-card input {
    width: 100%;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-size: 1.125rem;
    font-weight: 500;
    outline: none;
}

.input-card input::placeholder {
    color: var(--text-tertiary);
}

/* Course Headers */
.course-headers {
    display: grid;
    grid-template-columns: 2fr 2fr 2fr;
    gap: var(--space-md);
    margin-bottom: var(--space-md);
}

.header-item {
    color: var(--accent-blue);
    font-size: 1rem;
    font-weight: 700;
}

/* Course Row */
.course-row {
    display: grid;
    grid-template-columns: 2fr 2fr 2fr;
    gap: var(--space-md);
    margin-bottom: var(--space-md);
    animation: slideIn var(--transition-base);
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.course-row select {
    width: 100%;
    padding: var(--space-sm);
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-size: 0.95rem;
    cursor: pointer;
    transition: all var(--transition-fast);
    outline: none;
}

.course-row select:hover {
    border-color: var(--accent-orange);
}

.course-row select:focus {
    border-color: var(--accent-orange);
    box-shadow: 0 0 0 3px rgba(255, 152, 0, 0.1);
}

/* Retake Row */
.retake-row {
    margin-bottom: var(--space-lg);
    padding: var(--space-md);
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    animation: slideIn var(--transition-base);
}

.retake-headers {
    display: grid;
    grid-template-columns: 2fr 2fr 2fr;
    gap: var(--space-md);
    margin-bottom: var(--space-sm);
}

.retake-headers .header-item {
    font-size: 0.9rem;
}

.retake-inputs {
    display: grid;
    grid-template-columns: 2fr 2fr 2fr;
    gap: var(--space-md);
}

/* Action Buttons */
.action-buttons {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-sm);
    margin-bottom: var(--space-md);
}

.btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-xs);
    padding: var(--space-sm) var(--space-md);
    font-size: 0.875rem;
    font-weight: 700;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.btn-secondary {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background-color: var(--bg-tertiary);
    border-color: var(--accent-orange);
    transform: translateY(-2px);
}

.btn-primary {
    background: var(--gradient-orange);
    color: white;
    padding: var(--space-md);
    font-size: 1rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-orange);
    width: 100%;
}

.btn-primary:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(255, 152, 0, 0.4);
}

.btn-primary:active {
    transform: translateY(-1px);
}

.btn-primary.green {
    background: linear-gradient(135deg, #4CAF50, #388E3C);
    box-shadow: var(--shadow-green);
}

.btn-primary.green:hover {
    box-shadow: 0 6px 20px rgba(76, 175, 80, 0.4);
}

/* Result Card */
.result-card {
    background: var(--gradient-blue);
    border: 2px solid var(--accent-blue);
    border-radius: var(--radius-xl);
    padding: var(--space-lg);
    margin-top: var(--space-md);
    text-align: center;
    box-shadow: var(--shadow-blue);
    animation: scaleIn var(--transition-slow);
}

@keyframes scaleIn {
    from {
        opacity: 0;
        transform: scale(0.9);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

.result-card.hidden {
    display: none;
}

.result-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    color: var(--text-primary);
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--space-sm);
}

.star-icon {
    color: var(--accent-blue);
    transition: color var(--transition-base);
}

.result-card.excellent .star-icon {
    color: #FFC107;
}

.result-value {
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent-blue);
    margin: var(--space-sm) 0;
    text-shadow: 0 2px 10px rgba(33, 150, 243, 0.5);
    transition: color var(--transition-base);
}

.result-card.excellent .result-value {
    color: #FFC107;
    text-shadow: 0 2px 10px rgba(255, 193, 7, 0.5);
}

.result-description {
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-style: italic;
}

.perfect-badge {
    display: inline-block;
    margin-top: var(--space-sm);
    padding: var(--space-xs) var(--space-sm);
    background-color: rgba(255, 193, 7, 0.2);
    border: 1px solid #FFC107;
    border-radius: var(--radius-pill);
    color: #FFC107;
    font-size: 0.75rem;
    font-weight: 700;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.05);
    }
}

.perfect-badge.hidden {
    display: none;
}

/* ========================================
   GRADING TAB
   ======================================== */
.info-card {
    background: var(--gradient-blue);
    border: 2px solid var(--accent-blue);
    border-radius: var(--radius-xl);
    padding: var(--space-lg);
    text-align: center;
    margin-bottom: var(--space-lg);
}

.info-card.green {
    background: var(--gradient-green);
    border-color: var(--accent-green);
}

.info-card h2 {
    font-size: 1.25rem;
    font-weight: 700;
    margin: var(--space-sm) 0;
}

.info-card p {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

.grade-table-header {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-sm);
    padding: var(--space-md);
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    margin-bottom: var(--space-md);
}

.grade-header-item {
    color: var(--accent-blue);
    font-size: 1rem;
    font-weight: 700;
    text-align: center;
}

.grade-table {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
}

.grade-row {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-sm);
    padding: var(--space-md);
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
    animation: fadeIn var(--transition-base);
    animation-fill-mode: both;
}

.grade-row:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow-sm);
}

.grade-badge {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-xs) var(--space-sm);
    border-radius: var(--radius-sm);
    font-size: 1.125rem;
    font-weight: 700;
}

.grade-cgpa {
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-primary);
    font-size: 1.125rem;
    font-weight: 500;
}

.grade-mark {
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-secondary);
    font-size: 1rem;
}

/* ========================================
   TUITION TAB
   ======================================== */
.input-group {
    margin-bottom: var(--space-lg);
}

.input-group label {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: var(--space-sm);
}

.input-with-suffix {
    position: relative;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.input-with-suffix:hover {
    border-color: var(--accent-green);
}

.input-with-suffix:focus-within {
    border-color: var(--accent-green);
    box-shadow: 0 0 0 3px rgba(76, 175, 80, 0.1);
}

.input-with-suffix input {
    width: 100%;
    padding: var(--space-md);
    padding-right: 50px;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-size: 1.125rem;
    outline: none;
}

.input-with-suffix input::placeholder {
    color: var(--text-tertiary);
}

.suffix {
    position: absolute;
    right: var(--space-md);
    top: 50%;
    transform: translateY(-50%);
    color: var(--accent-green);
    font-weight: 700;
    pointer-events: none;
}

/* Waiver Options */
.waiver-options {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-xs);
}

.waiver-btn {
    padding: var(--space-xs) var(--space-md);
    background: transparent;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-pill);
    color: var(--text-secondary);
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.waiver-btn:hover {
    border-color: var(--accent-green);
    color: var(--text-primary);
}

.waiver-btn.active {
    background-color: var(--accent-green);
    border-color: var(--accent-green);
    color: white;
}

.custom-waiver-input {
    margin-top: var(--space-md);
    animation: slideIn var(--transition-base);
}

.custom-waiver-input.hidden {
    display: none;
}

/* Tuition Results */
.tuition-results {
    margin-top: var(--space-lg);
    animation: fadeIn var(--transition-base);
}

.tuition-results.hidden {
    display: none;
}

.payable-card {
    background: var(--gradient-green);
    border: 2px solid var(--accent-green);
    border-radius: var(--radius-xl);
    padding: var(--space-lg);
    text-align: center;
    margin-bottom: var(--space-lg);
    box-shadow: var(--shadow-green);
}

.payable-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    color: var(--text-primary);
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: var(--space-sm);
}

.payable-value {
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--accent-green);
    margin: var(--space-sm) 0;
    text-shadow: 0 2px 10px rgba(76, 175, 80, 0.5);
}

.payable-info {
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-style: italic;
}

.installments-title {
    color: var(--text-primary);
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: var(--space-md);
    text-align: center;
}

.installment-card {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    padding: var(--space-md);
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    margin-bottom: var(--space-sm);
    transition: all var(--transition-fast);
    animation: slideIn var(--transition-base);
}

.installment-card:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow-sm);
}

.installment-card.blue {
    border-color: rgba(33, 150, 243, 0.5);
}

.installment-card.orange {
    border-color: rgba(255, 152, 0, 0.5);
}

.installment-card.purple {
    border-color: rgba(156, 39, 176, 0.5);
}

.installment-icon {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border-radius: var(--radius-md);
    flex-shrink: 0;
}

.installment-card.blue .installment-icon {
    background-color: rgba(33, 150, 243, 0.2);
}

.installment-card.orange .installment-icon {
    background-color: rgba(255, 152, 0, 0.2);
}

.installment-card.purple .installment-icon {
    background-color: rgba(156, 39, 176, 0.2);
}

.installment-content {
    flex: 1;
}

.installment-title {
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 4px;
}

.installment-amount {
    font-size: 1.125rem;
    font-weight: 700;
}

.installment-card.blue .installment-amount {
    color: var(--accent-blue);
}

.installment-card.orange .installment-amount {
    color: var(--accent-orange);
}

.installment-card.purple .installment-amount {
    color: var(--accent-purple);
}

/* ========================================
   MODAL
   ======================================== */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.7);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    padding: var(--space-md);
    opacity: 1;
    transition: opacity var(--transition-base);
}

.modal.hidden {
    opacity: 0;
    pointer-events: none;
}

.modal-content {
    background-color: var(--bg-secondary);
    border-radius: var(--radius-xl);
    max-width: 600px;
    width: 100%;
    max-height: 80vh;
    overflow: hidden;
    box-shadow: var(--shadow-lg);
    animation: modalSlideIn var(--transition-base);
}

@keyframes modalSlideIn {
    from {
        opacity: 0;
        transform: translateY(-50px) scale(0.9);
    }
    to {
        opacity: 1;
        transform: translateY(0) scale(1);
    }
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-lg);
    border-bottom: 1px solid var(--border-color);
}

.modal-header h2 {
    font-size: 1.5rem;
    font-weight: 700;
}

.close-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    font-size: 2rem;
    cursor: pointer;
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.close-btn:hover {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

.modal-body {
    padding: var(--space-lg);
    overflow-y: auto;
    max-height: calc(80vh - 100px);
}

.modal-body h3 {
    font-size: 1.125rem;
    font-weight: 700;
    margin-top: var(--space-lg);
    margin-bottom: var(--space-sm);
    color: var(--accent-orange);
}

.modal-body p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: var(--space-md);
}

.contact-info {
    display: flex;
    flex-direction: column;
    gap: var(--space-lg);
}

.contact-item {
    display: flex;
    gap: var(--space-md);
    padding: var(--space-md);
    background-color: var(--bg-tertiary);
    border-radius: var(--radius-lg);
    transition: all var(--transition-fast);
}

.contact-item:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow-sm);
}

.contact-item strong {
    display: block;
    color: var(--text-primary);
    margin-bottom: 4px;
}

.contact-item p {
    color: var(--text-secondary);
    margin: 0;
}

/* ========================================
   RESPONSIVE DESIGN
   ======================================== */
@media (max-width: 768px) {
    .header-content {
        padding: var(--space-sm) var(--space-md);
    }
    
    .app-title {
        font-size: 1.125rem;
    }
    
    .tabs {
        overflow-x: auto;
    }
    
    .tab {
        padding: var(--space-sm);
        font-size: 0.75rem;
        white-space: nowrap;
    }
    
    .main-content {
        padding: var(--space-md);
    }
    
    .action-buttons {
        grid-template-columns: 1fr;
    }
    
    .course-headers {
        grid-template-columns: 1fr 1fr 1fr;
        gap: var(--space-xs);
    }
    
    .course-row {
        grid-template-columns: 1fr 1fr 1fr;
        gap: var(--space-xs);
    }
    
    .header-item {
        font-size: 0.875rem;
    }
    
    .result-value {
        font-size: 2.5rem;
    }
    
    .waiver-options {
        gap: var(--space-xs);
    }
    
    .waiver-btn {
        padding: var(--space-xs) var(--space-sm);
        font-size: 0.875rem;
    }
}

@media (max-width: 480px) {
    .input-row {
        grid-template-columns: 1fr;
    }
    
    .course-row select {
        font-size: 0.875rem;
        padding: var(--space-xs);
    }
    
    .modal-content {
        max-height: 90vh;
    }
}

/* ========================================
   UTILITY CLASSES
   ======================================== */
.hidden {
    display: none !important;
}

/* Scrollbar Styling */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: var(--radius-sm);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-tertiary);
}