/* ============================================
   ROOT & VARIABLES
   ============================================ */
:root {
    --bg-primary: #0b0b0b;
    --bg-secondary: #1a1a1a;
    --card-bg: rgba(255, 255, 255, 0.05);
    --card-bg-hover: rgba(255, 255, 255, 0.08);
    --accent: #4f46e5;
    --accent-hover: #4340d1;
    --success: #22c55e;
    --success-hover: #16a34a;
    --danger: #ef4444;
    --danger-hover: #dc2626;
    --text-primary: #ffffff;
    --text-secondary: #a0aec0;
    --text-tertiary: #64748b;
    --border-color: rgba(255, 255, 255, 0.1);
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.3), 0 1px 3px rgba(0, 0, 0, 0.2);
    --shadow-lg: 0 20px 25px rgba(0, 0, 0, 0.4), 0 10px 10px rgba(0, 0, 0, 0.2);
    --shadow-xl: 0 25px 50px rgba(0, 0, 0, 0.5);
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* ============================================
   ANIMATIONS
   ============================================ */
@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

@keyframes slideInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

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

@keyframes scaleIn {
    from {
        opacity: 0;
        transform: scale(0.95);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

@keyframes float {
    0%, 100% {
        transform: translateY(0px);
    }
    50% {
        transform: translateY(-20px);
    }
}

@keyframes glow {
    0%, 100% {
        opacity: 0.5;
    }
    50% {
        opacity: 1;
    }
}

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

@keyframes shimmer {
    0% {
        background-position: -1000px 0;
    }
    100% {
        background-position: 1000px 0;
    }
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
        'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
        sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    overflow-x: hidden;
    animation: fadeIn 0.8s ease-out;
}

/* ============================================
   BACKGROUND DECORATION
   ============================================ */
.background-decoration {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: -1;
}

.blur-circle {
    position: absolute;
    border-radius: 50%;
    filter: blur(80px);
    opacity: 0.1;
    animation: float 20s ease-in-out infinite;
}

.blur-1 {
    width: 400px;
    height: 400px;
    top: -100px;
    left: -100px;
    background: radial-gradient(circle, var(--accent), transparent);
    animation-delay: 0s;
}

.blur-2 {
    width: 300px;
    height: 300px;
    top: 50%;
    right: -50px;
    background: radial-gradient(circle, var(--success), transparent);
    animation-delay: 5s;
}

.blur-3 {
    width: 350px;
    height: 350px;
    bottom: -100px;
    left: 20%;
    background: radial-gradient(circle, var(--danger), transparent);
    animation-delay: 10s;
}

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

@media (max-width: 768px) {
    .container {
        padding: var(--spacing-lg);
    }
}

@media (max-width: 480px) {
    .container {
        padding: var(--spacing-md);
    }
}

/* ============================================
   HEADER
   ============================================ */
.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    animation: slideInDown 0.6s ease-out;
}

.header-content {
    position: relative;
    z-index: 1;
}

.header-title {
    font-size: 3.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: var(--spacing-md);
    background: linear-gradient(135deg, var(--text-primary), var(--text-secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.header-subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
    font-weight: 400;
}

@media (max-width: 768px) {
    .header-title {
        font-size: 2.5rem;
    }

    .header-subtitle {
        font-size: 1rem;
    }
}

/* ============================================
   MAIN CONTENT
   ============================================ */
.main-content {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-2xl);
}

/* ============================================
   SECTIONS
   ============================================ */
.section {
    animation: slideInUp 0.6s ease-out;
}

.section:nth-child(2) {
    animation-delay: 0.1s;
}

.section:nth-child(3) {
    animation-delay: 0.2s;
}

.section:nth-child(4) {
    animation-delay: 0.3s;
}

.section:nth-child(5) {
    animation-delay: 0.4s;
}

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

.section-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

@media (max-width: 480px) {
    .section-title {
        font-size: 1.25rem;
    }

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

/* ============================================
   CARDS
   ============================================ */
.card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    transition: all var(--transition-base);
    box-shadow: var(--shadow-md);
}

.card:hover {
    background: var(--card-bg-hover);
    border-color: rgba(255, 255, 255, 0.15);
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

/* ============================================
   FORM
   ============================================ */
.form {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-lg);
}

@media (max-width: 768px) {
    .form {
        grid-template-columns: 1fr;
    }
}

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

.form-group:last-child {
    grid-column: 1 / -1;
}

.form-label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-primary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.form-input {
    background: rgba(255, 255, 255, 0.08);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    color: var(--text-primary);
    font-size: 1rem;
    font-family: inherit;
    transition: all var(--transition-base);
}

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

.form-input:focus {
    outline: none;
    background: rgba(255, 255, 255, 0.1);
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

.form-input:hover {
    border-color: rgba(255, 255, 255, 0.2);
}

/* ============================================
   BUTTONS
   ============================================ */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: 0.95rem;
    font-weight: 600;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    text-decoration: none;
    white-space: nowrap;
    user-select: none;
}

.btn:active {
    transform: scale(0.98);
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent), #5a51f5);
    color: white;
    box-shadow: 0 4px 15px rgba(79, 70, 229, 0.3);
}

.btn-primary:hover {
    background: linear-gradient(135deg, var(--accent-hover), #4a41e5);
    box-shadow: 0 6px 20px rgba(79, 70, 229, 0.4);
    transform: translateY(-2px);
}

.btn-secondary {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    box-shadow: none;
}

.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.08);
    border-color: rgba(255, 255, 255, 0.2);
}

.btn-danger {
    background: rgba(239, 68, 68, 0.2);
    color: var(--danger);
    border: 1px solid rgba(239, 68, 68, 0.3);
}

.btn-danger:hover {
    background: rgba(239, 68, 68, 0.3);
    border-color: var(--danger);
}

.btn-block {
    width: 100%;
}

.btn-sm {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.875rem;
}

.btn-icon {
    font-weight: 700;
}

/* ============================================
   SUMMARY GRID
   ============================================ */
.summary-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
}

@media (max-width: 768px) {
    .summary-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .summary-grid {
        grid-template-columns: 1fr;
    }
}

.summary-card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    text-align: center;
    transition: all var(--transition-base);
    animation: slideInUp 0.6s ease-out;
}

.summary-card:nth-child(1) {
    animation-delay: 0.05s;
}

.summary-card:nth-child(2) {
    animation-delay: 0.1s;
}

.summary-card:nth-child(3) {
    animation-delay: 0.15s;
}

.summary-card:nth-child(4) {
    animation-delay: 0.2s;
}

.summary-card:nth-child(5) {
    animation-delay: 0.25s;
}

.summary-card:nth-child(6) {
    animation-delay: 0.3s;
}

.summary-card:hover {
    background: var(--card-bg-hover);
    border-color: rgba(255, 255, 255, 0.15);
    transform: translateY(-8px);
}

.summary-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--spacing-md);
}

.summary-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--accent);
    letter-spacing: -0.01em;
}

/* ============================================
   INSIGHTS
   ============================================ */
.insights-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
}

@media (max-width: 768px) {
    .insights-grid {
        grid-template-columns: 1fr;
    }
}

.insight-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    gap: var(--spacing-md);
    padding: var(--spacing-xl) var(--spacing-lg);
}

.insight-icon {
    font-size: 2.5rem;
}

.insight-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.insight-value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

/* ============================================
   SETTLEMENT
   ============================================ */
.settlement-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.settlement-item {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: all var(--transition-base);
    animation: slideInUp 0.4s ease-out;
}

.settlement-item:hover {
    background: var(--card-bg-hover);
    border-color: rgba(255, 255, 255, 0.15);
    transform: translateX(4px);
}

.settlement-text {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    flex: 1;
}

.settlement-emoji {
    font-size: 1.5rem;
}

.settlement-info {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.settlement-from {
    font-weight: 600;
    color: var(--text-primary);
}

.settlement-amount {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--accent);
}

.empty-state {
    text-align: center;
    padding: var(--spacing-2xl) var(--spacing-lg);
    color: var(--text-secondary);
}

/* ============================================
   EXPENSE HISTORY
   ============================================ */
.expense-history {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.expense-card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    gap: var(--spacing-lg);
    transition: all var(--transition-base);
    animation: slideInUp 0.4s ease-out;
}

.expense-card:hover {
    background: var(--card-bg-hover);
    border-color: rgba(255, 255, 255, 0.15);
    transform: translateY(-4px);
}

.expense-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

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

.expense-person {
    font-weight: 700;
    font-size: 1.125rem;
    color: var(--text-primary);
    background: linear-gradient(135deg, var(--accent), #5a51f5);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    min-width: 2rem;
    text-align: center;
}

.expense-description {
    color: var(--text-secondary);
    font-weight: 500;
}

.expense-date {
    font-size: 0.875rem;
    color: var(--text-tertiary);
}

.expense-amount {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--success);
    min-width: 100px;
    text-align: right;
}

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

@media (max-width: 480px) {
    .expense-card {
        flex-direction: column;
        gap: var(--spacing-md);
    }

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

    .expense-amount {
        width: 100%;
    }
}

/* ============================================
   FOOTER
   ============================================ */
.footer {
    text-align: center;
    padding: var(--spacing-2xl) 0 var(--spacing-lg);
    color: var(--text-tertiary);
    border-top: 1px solid var(--border-color);
    margin-top: var(--spacing-2xl);
    font-size: 0.875rem;
}

/* ============================================
   RESPONSIVE
   ============================================ */
@media (max-width: 768px) {
    .summary-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .summary-grid {
        grid-template-columns: 1fr;
    }

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

    .blur-1 {
        width: 250px;
        height: 250px;
    }

    .blur-2 {
        width: 200px;
        height: 200px;
    }

    .blur-3 {
        width: 200px;
        height: 200px;
    }
}

/* ============================================
   UTILITIES
   ============================================ */
.text-center {
    text-align: center;
}

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

.mt-lg {
    margin-top: var(--spacing-lg);
}

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

/* ============================================
   SCROLLBAR
   ============================================ */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.1);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 255, 255, 0.2);
}