:root {
    --primary-color: #6366F1;
    --primary-dark: #4F46E5;
    --primary-light: #8B5CF6;
    --secondary-color: #10B981;
    --secondary-dark: #059669;
    --accent-color: #F59E0B;
    --danger-color: #EF4444;
    --warning-color: #F59E0B;
    --success-color: #10B981;
    
    --background-color: #0F172A;
    --surface-color: #1E293B;
    --card-color: #334155;
    --text-primary: #F1F5F9;
    --text-secondary: #94A3B8;
    --text-muted: #64748B;
    --border-color: #475569;
    --hover-color: #475569;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    --border-radius: 12px;
    --border-radius-sm: 8px;
    --border-radius-lg: 16px;
    
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, var(--background-color) 0%, #1E293B 100%);
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Cards */
.card {
    background: var(--card-color);
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-xl);
    margin-bottom: 24px;
    overflow: hidden;
    transition: var(--transition);
    border: 1px solid var(--border-color);
}

.card:hover {
    transform: translateY(-2px);
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
}

.card-header {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-light));
    color: white;
    padding: 24px;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.card-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: linear-gradient(45deg, transparent, rgba(255,255,255,0.1), transparent);
    transform: translateX(-100%);
}

.card-header:hover::before {
    transform: translateX(100%);
    transition: transform 0.6s ease;
}

.card-header h1 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 8px;
    text-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.card-header p {
    font-size: 1.1rem;
    opacity: 0.9;
    margin-bottom: 4px;
}

.card-body {
    padding: 28px;
}

/* Forms */
.form-group {
    margin-bottom: 24px;
}

.form-control {
    width: 100%;
    padding: 14px 16px;
    background: var(--surface-color);
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: 16px;
    color: var(--text-primary);
    transition: var(--transition);
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
    background: var(--surface-color);
}

.form-control::placeholder {
    color: var(--text-muted);
}

.form-control:disabled {
    background: var(--background-color);
    color: var(--text-muted);
    cursor: not-allowed;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text-primary);
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* Buttons */
.btn {
    padding: 14px 28px;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 16px;
    font-weight: 600;
    transition: var(--transition);
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255,255,255,0.2), transparent);
    transition: left 0.5s ease;
}

.btn:hover::before {
    left: 100%;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
}

.btn-primary:hover {
    background: linear-gradient(135deg, var(--primary-dark), var(--primary-color));
    box-shadow: 0 8px 25px rgba(99, 102, 241, 0.3);
}

.btn-secondary {
    background: var(--surface-color);
    color: var(--text-primary);
    border: 2px solid var(--border-color);
}

.btn-secondary:hover {
    background: var(--hover-color);
    border-color: var(--primary-color);
}

.btn-success {
    background: linear-gradient(135deg, var(--success-color), var(--secondary-dark));
    color: white;
}

.btn-success:hover {
    background: linear-gradient(135deg, var(--secondary-dark), var(--success-color));
    box-shadow: 0 8px 25px rgba(16, 185, 129, 0.3);
}

.btn-warning {
    background: linear-gradient(135deg, var(--warning-color), #D97706);
    color: white;
}

.btn-warning:hover {
    background: linear-gradient(135deg, #D97706, var(--warning-color));
    box-shadow: 0 8px 25px rgba(245, 158, 11, 0.3);
}

.btn-danger {
    background: linear-gradient(135deg, var(--danger-color), #DC2626);
    color: white;
}

.btn-danger:hover {
    background: linear-gradient(135deg, #DC2626, var(--danger-color));
    box-shadow: 0 8px 25px rgba(239, 68, 68, 0.3);
}

.btn-sm {
    padding: 10px 20px;
    font-size: 14px;
}

/* Tables */
.table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
    background: var(--surface-color);
    border-radius: var(--border-radius);
    overflow: hidden;
    box-shadow: var(--shadow-md);
}

.table th,
.table td {
    padding: 16px 20px;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.table th {
    background: var(--card-color);
    font-weight: 600;
    color: var(--text-primary);
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.table td {
    color: var(--text-secondary);
}

.table tbody tr {
    transition: var(--transition);
}

.table tbody tr:hover {
    background: var(--hover-color);
    transform: translateX(4px);
}

.table-responsive {
    overflow-x: auto;
    border-radius: var(--border-radius);
}

/* Navigation */
.navbar {
    background: var(--card-color);
    padding: 0;
    margin-bottom: 32px;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
}

.nav-menu {
    display: flex;
    justify-content: center;
    list-style: none;
    gap: 8px;
    padding: 8px;
}

.nav-menu a {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 600;
    padding: 12px 24px;
    border-radius: var(--border-radius);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.nav-menu a::before {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    width: 0;
    height: 2px;
    background: var(--primary-color);
    transition: var(--transition);
    transform: translateX(-50%);
}

.nav-menu a:hover,
.nav-menu a.active {
    color: var(--text-primary);
    background: var(--surface-color);
}

.nav-menu a:hover::before,
.nav-menu a.active::before {
    width: 80%;
}

.nav-menu a.active {
    color: var(--primary-color);
}

/* Accordion */
.accordion-header {
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 0;
    transition: var(--transition);
    user-select: none;
    border-bottom: 2px solid transparent;
}

.accordion-header:hover {
    background: var(--surface-color);
    margin: -20px;
    padding: 20px;
    border-radius: var(--border-radius);
    border-bottom-color: var(--primary-color);
}

.accordion-header h3 {
    margin: 0;
    color: var(--text-primary);
    font-size: 1.4em;
    font-weight: 700;
}

.accordion-icon {
    font-size: 1.5em;
    font-weight: bold;
    color: var(--primary-color);
    transition: var(--transition);
    min-width: 30px;
    text-align: center;
}

.accordion-content {
    animation: fadeIn 0.3s ease;
    margin-top: 20px;
}

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

/* Debt List */
.debt-list {
    list-style: none;
    margin-top: 20px;
}

.debt-item {
    background: var(--surface-color);
    padding: 20px;
    margin-bottom: 16px;
    border-radius: var(--border-radius);
    border-left: 4px solid var(--primary-color);
    transition: var(--transition);
    box-shadow: var(--shadow-md);
}

.debt-item:hover {
    transform: translateX(8px);
    box-shadow: var(--shadow-lg);
}

.debt-settled {
    background: rgba(16, 185, 129, 0.1);
    border-left-color: var(--success-color);
    opacity: 0.8;
}

.settled-badge {
    background: var(--success-color);
    color: white;
    padding: 8px 16px;
    border-radius: 20px;
    font-size: 0.8em;
    font-weight: bold;
    text-align: center;
    box-shadow: var(--shadow-sm);
}

/* Progress Bar */
.progress-container {
    background: var(--surface-color);
    border-radius: 10px;
    height: 12px;
    overflow: hidden;
    margin: 16px 0;
    box-shadow: inset 0 2px 4px rgba(0,0,0,0.1);
}

.progress-bar {
    background: linear-gradient(90deg, var(--success-color), var(--secondary-dark));
    height: 100%;
    transition: width 0.5s ease;
    position: relative;
    overflow: hidden;
}

.progress-bar::after {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255,255,255,0.3), transparent);
    animation: shimmer 2s infinite;
}

@keyframes shimmer {
    0% { left: -100%; }
    100% { left: 100%; }
}

/* Alerts */
.alert {
    padding: 16px 20px;
    border-radius: var(--border-radius);
    margin-bottom: 20px;
    border-left: 4px solid;
    box-shadow: var(--shadow-md);
}

.alert-success {
    background: rgba(16, 185, 129, 0.1);
    color: var(--success-color);
    border-left-color: var(--success-color);
}

.alert-error {
    background: rgba(239, 68, 68, 0.1);
    color: var(--danger-color);
    border-left-color: var(--danger-color);
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(8px);
}

.modal-content {
    background: var(--card-color);
    margin: 10% auto;
    padding: 32px;
    border-radius: var(--border-radius-lg);
    width: 90%;
    max-width: 500px;
    box-shadow: var(--shadow-xl);
    border: 1px solid var(--border-color);
    animation: modalSlideIn 0.3s ease;
    position: relative;
}

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

.close {
    font-size: 28px;
    font-weight: bold;
    cursor: pointer;
    color: var(--text-muted);
    transition: var(--transition);
    position: absolute;
    top: 20px;
    right: 24px;
}

.close:hover {
    color: var(--danger-color);
    transform: rotate(90deg);
}

/* Form inline */
.form-inline {
    display: flex;
    gap: 12px;
    align-items: flex-end;
    flex-wrap: wrap;
}

.form-inline .form-control {
    flex: 1;
    min-width: 200px;
}

/* Event controls */
.event-controls {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    align-items: flex-end;
}

/* Login container */
.login-container {
    max-width: 400px;
    margin: 100px auto;
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 16px;
    }
    
    .card-body {
        padding: 20px;
    }
    
    .nav-menu {
        flex-direction: column;
        gap: 4px;
    }
    
    .nav-menu a {
        text-align: center;
        padding: 16px;
    }
    
    .form-inline {
        flex-direction: column;
    }
    
    .form-inline .form-control {
        min-width: 100%;
    }
    
    .event-controls {
        flex-direction: column;
    }
    
    .table {
        font-size: 14px;
    }
    
    .table th,
    .table td {
        padding: 12px 8px;
    }
    
    .btn {
        width: 100%;
        margin-bottom: 8px;
    }
    
    .modal-content {
        margin: 20% auto;
        padding: 24px;
    }
    
    .accordion-header {
        padding: 16px 0;
    }
    
    .accordion-header:hover {
        margin: -16px;
        padding: 16px;
    }
}

@media (max-width: 480px) {
    .card-header h1 {
        font-size: 1.5rem;
    }
    
    .card-header p {
        font-size: 0.9rem;
    }
    
    .table {
        font-size: 12px;
    }
    
    .table th,
    .table td {
        padding: 8px 4px;
    }
}

/* Utility classes */
.text-center { text-align: center; }
.text-right { text-align: right; }
.text-left { text-align: left; }
.mb-0 { margin-bottom: 0; }
.mt-0 { margin-top: 0; }
.mb-4 { margin-bottom: 24px; }
.mt-4 { margin-top: 24px; }

/* Custom scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--surface-color);
}

::-webkit-scrollbar-thumb {
    background: var(--primary-color);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--primary-dark);
}