/* ========== BASE STYLES ========== */
:root {
    /* Color Palette */
    --primary: #1A535C;
    --secondary: #4ECDC4;
    --light: #F7FFF7;
    --accent: #FF6B6B;
    --highlight: #FFE66D;
    
    /* Light Theme Colors */
    --background: var(--light);
    --text: #333333;
    --card-bg: #ffffff;
    --border: #e0e0e0;
    --input-bg: #ffffff;
    --shadow: rgba(0, 0, 0, 0.1);
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    
    /* Typography */
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    --font-size-sm: 0.875rem;
    --font-size-md: 1rem;
    --font-size-lg: 1.25rem;
    --font-size-xl: 1.5rem;
    --font-size-xxl: 2rem;
    
    /* Border Radius */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 12px;
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    
    /* Layout */
    --header-height: 60px;
    --footer-height: 50px;
    --mobile-nav-height: 60px;
}

/* Dark Theme Colors */
.dark-theme {
    --background: #121212;
    --text: #f5f5f5;
    --card-bg: #1e1e1e;
    --border: #333333;
    --input-bg: #2c2c2c;
    --shadow: rgba(0, 0, 0, 0.3);
}

/* Reset and 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(--background);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    transition: background-color var(--transition-normal);
}

a {
    color: var(--secondary);
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

ul {
    list-style: none;
}

img {
    max-width: 100%;
    height: auto;
}

button, input, select, textarea {
    font-family: inherit;
    font-size: inherit;
}

/* ========== LAYOUT ========== */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.app-header {
    height: var(--header-height);
    background-color: var(--primary);
    color: white;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    box-shadow: 0 2px 4px var(--shadow);
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 100%;
}

.app-title {
    font-size: var(--font-size-xl);
    font-weight: bold;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.app-title i {
    color: var(--highlight);
}

.main-nav {
    display: flex;
    align-items: center;
}

#app-container {
    flex: 1;
    margin-top: var(--header-height);
    margin-bottom: var(--mobile-nav-height);
    padding: var(--spacing-md) 0;
    position: relative;
    overflow-x: hidden;
}

.app-footer {
    background-color: var(--primary);
    color: white;
    text-align: center;
    padding: var(--spacing-md) 0;
    font-size: var(--font-size-sm);
    position: relative;
    z-index: 10;
}

.mobile-nav {
    display: flex;
    justify-content: space-around;
    align-items: center;
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    height: var(--mobile-nav-height);
    background-color: var(--card-bg);
    box-shadow: 0 -2px 10px var(--shadow);
    z-index: 90;
}

/* ========== COMPONENTS ========== */
/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--border-radius-md);
    border: none;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    white-space: nowrap;
}

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

.btn-primary:hover {
    background-color: #15444a;
}

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

.btn-secondary:hover {
    background-color: #3db5ae;
}

.btn-danger {
    background-color: var(--accent);
    color: white;
}

.btn-danger:hover {
    background-color: #e55b5b;
}

.btn-text {
    background: transparent;
    color: var(--text);
    padding: var(--spacing-xs) var(--spacing-sm);
}

.btn-text:hover {
    background-color: rgba(0, 0, 0, 0.05);
}

.btn-icon {
    background: transparent;
    border: none;
    color: white;
    font-size: var(--font-size-lg);
    cursor: pointer;
    padding: var(--spacing-xs);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color var(--transition-fast);
}

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

.btn-block {
    width: 100%;
}

/* Forms */
.app-form {
    background-color: var(--card-bg);
    padding: var(--spacing-lg);
    border-radius: var(--border-radius-md);
    box-shadow: 0 2px 10px var(--shadow);
    margin-bottom: var(--spacing-lg);
}

.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-group label {
    display: block;
    margin-bottom: var(--spacing-xs);
    font-weight: 500;
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border);
    border-radius: var(--border-radius-sm);
    background-color: var(--input-bg);
    color: var(--text);
    transition: border-color var(--transition-fast);
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--secondary);
}

.participant-input-group {
    display: flex;
    gap: var(--spacing-sm);
}

.participant-input-group input {
    flex: 1;
}

.participants-list {
    margin-top: var(--spacing-md);
}

.participant-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-sm);
    background-color: var(--input-bg);
    border-radius: var(--border-radius-sm);
    margin-bottom: var(--spacing-xs);
}

.participant-name {
    font-weight: 500;
}

.remove-participant {
    color: var(--accent);
    background: none;
    border: none;
    cursor: pointer;
    font-size: var(--font-size-md);
}

.checkbox-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
    margin-bottom: var(--spacing-sm);
}

.checkbox-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.checkbox-item input[type="checkbox"] {
    width: auto;
}

.participant-actions {
    display: flex;
    gap: var(--spacing-md);
    margin-top: var(--spacing-xs);
}

.currency-input {
    position: relative;
    display: flex;
    align-items: center;
}

.currency-input span {
    position: absolute;
    left: var(--spacing-md);
    color: var(--text);
    opacity: 0.7;
}

.currency-input input {
    padding-left: 2.5rem !important;
}

.form-actions {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

/* Cards */
.card {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    box-shadow: 0 2px 8px var(--shadow);
    padding: var(--spacing-lg);
    margin-bottom: var(--spacing-md);
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--shadow);
}

.trip-card {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.trip-card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
}

.trip-name {
    font-size: var(--font-size-lg);
    font-weight: bold;
    margin-right: var(--spacing-sm);
}

.trip-date {
    font-size: var(--font-size-sm);
    color: var(--text);
    opacity: 0.7;
}

.trip-info {
    display: flex;
    gap: var(--spacing-lg);
    margin: var(--spacing-sm) 0;
}

.info-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    font-size: var(--font-size-sm);
}

.trip-actions {
    display: flex;
    gap: var(--spacing-sm);
    margin-top: var(--spacing-sm);
}

.expense-card {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    box-shadow: 0 2px 6px var(--shadow);
    margin-bottom: var(--spacing-md);
    transition: transform var(--transition-fast);
}

.expense-card:hover {
    transform: translateY(-2px);
}

.expense-details {
    flex: 1;
}

.expense-title {
    font-weight: bold;
    margin-bottom: var(--spacing-xs);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.expense-category-icon {
    color: var(--secondary);
}

.expense-meta {
    font-size: var(--font-size-sm);
    color: var(--text);
    opacity: 0.7;
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.expense-amount {
    font-weight: bold;
    font-size: var(--font-size-lg);
    color: var(--primary);
}

.expense-actions {
    display: flex;
    gap: var(--spacing-xs);
}

/* Tabs */
.trip-tabs {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    border-bottom: 1px solid var(--border);
    overflow-x: auto;
    scrollbar-width: none;
    -ms-overflow-style: none;
}

.trip-tabs::-webkit-scrollbar {
    display: none;
}

.tab-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    background: transparent;
    border: none;
    color: var(--text);
    font-weight: 500;
    cursor: pointer;
    position: relative;
    white-space: nowrap;
}

.tab-btn.active {
    color: var(--secondary);
}

.tab-btn.active::after {
    content: '';
    position: absolute;
    bottom: -1px;
    left: 0;
    right: 0;
    height: 3px;
    background-color: var(--secondary);
    border-radius: 3px 3px 0 0;
}

.tab-content {
    display: none;
}

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

/* Summary Cards */
.summary-totals {
    display: flex;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.summary-card {
    flex: 1;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    box-shadow: 0 2px 8px var(--shadow);
    text-align: center;
}

.summary-card h3 {
    font-size: var(--font-size-md);
    margin-bottom: var(--spacing-sm);
    color: var(--text);
}

.total-amount {
    font-size: var(--font-size-xl);
    font-weight: bold;
    color: var(--primary);
}

.avg-amount {
    font-size: var(--font-size-xl);
    font-weight: bold;
    color: var(--secondary);
}

.balance-list {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    box-shadow: 0 2px 8px var(--shadow);
    margin-bottom: var(--spacing-lg);
}

.balance-item {
    padding: var(--spacing-sm) 0;
    border-bottom: 1px solid var(--border);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

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

.balance-amount {
    font-weight: bold;
}

.balance-positive {
    color: #4CAF50;
}

.balance-negative {
    color: var(--accent);
}

.balance-neutral {
    color: #9E9E9E;
}

.summary-actions {
    display: flex;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
}

/* Charts */
.charts-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.chart-card {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    box-shadow: 0 2px 8px var(--shadow);
}

.chart-card h3 {
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.chart-wrapper {
    height: 300px;
    position: relative;
}

/* Settings */
.settings-list {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    box-shadow: 0 2px 8px var(--shadow);
    margin-bottom: var(--spacing-lg);
}

.settings-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--border);
}

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

.settings-label {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

.settings-label i {
    color: var(--secondary);
    font-size: var(--font-size-lg);
    width: 24px;
    text-align: center;
}

.settings-select {
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--border-radius-sm);
    border: 1px solid var(--border);
    background-color: var(--input-bg);
    color: var(--text);
}

.about-section {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-lg);
    box-shadow: 0 2px 8px var(--shadow);
    text-align: center;
}

.about-section h3 {
    margin-bottom: var(--spacing-md);
}

.about-section p {
    margin-bottom: var(--spacing-sm);
    color: var(--text);
    opacity: 0.8;
}

/* Switch Toggle */
.switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: #ccc;
    transition: var(--transition-normal);
}

.slider:before {
    position: absolute;
    content: "";
    height: 16px;
    width: 16px;
    left: 4px;
    bottom: 4px;
    background-color: white;
    transition: var(--transition-normal);
}

input:checked + .slider {
    background-color: var(--secondary);
}

input:focus + .slider {
    box-shadow: 0 0 1px var(--secondary);
}

input:checked + .slider:before {
    transform: translateX(26px);
}

.slider.round {
    border-radius: 24px;
}

.slider.round:before {
    border-radius: 50%;
}

/* Empty States */
.empty-state {
    text-align: center;
    padding: var(--spacing-xl) 0;
    color: var(--text);
    opacity: 0.7;
}

.empty-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    color: var(--border);
}

/* Mobile Navigation */
.nav-btn {
    background: transparent;
    border: none;
    color: var(--text);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) 0;
    width: 33%;
    transition: color var(--transition-fast);
}

.nav-btn i {
    font-size: var(--font-size-lg);
}

.nav-btn span {
    font-size: var(--font-size-sm);
}

.nav-btn.active {
    color: var(--secondary);
}

/* Screens */
.screen {
    display: none;
    animation: fadeIn 0.3s ease;
}

.screen.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.screen-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
}

.expenses-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-md);
}

.expenses-filter {
    position: relative;
}

.filter-select {
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--border-radius-sm);
    border: 1px solid var(--border);
    background-color: var(--input-bg);
    color: var(--text);
}

.filter-options {
    position: absolute;
    top: 100%;
    left: 0;
    z-index: 10;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-sm);
    box-shadow: 0 2px 10px var(--shadow);
    width: 200px;
    margin-top: var(--spacing-xs);
    padding: var(--spacing-xs);
}

/* Utility Classes */
.hidden {
    display: none !important;
}

.text-center {
    text-align: center;
}

.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }
.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }

/* ========== RESPONSIVE STYLES ========== */
@media (min-width: 768px) {
    .mobile-nav {
        display: none;
    }
    
    #app-container {
        margin-bottom: 0;
    }
    
    .summary-totals {
        flex-direction: row;
    }
    
    .charts-container {
        flex-direction: row;
    }
    
    .chart-card {
        flex: 1;
    }
}

@media (max-width: 767px) {
    .app-title {
        font-size: var(--font-size-lg);
    }
    
    .summary-totals {
        flex-direction: column;
    }
    
    .summary-actions {
        flex-direction: column;
    }
    
    .expense-card {
        flex-direction: column;
        align-items: flex-start;
    }
    
    .expense-amount {
        margin-top: var(--spacing-sm);
    }
    
    .expense-actions {
        margin-top: var(--spacing-sm);
        align-self: flex-end;
    }
}

@media (max-width: 480px) {
    :root {
        --spacing-md: 0.75rem;
        --spacing-lg: 1.25rem;
    }
    
    .app-form {
        padding: var(--spacing-md);
    }
    
    .screen-header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-sm);
    }
    
    .screen-header button {
        align-self: flex-end;
    }
}