/* ==========================================
   ENTERPRISE BILLING SYSTEM - STYLES
   Modern, secure, and responsive design
   ========================================== */

:root {
    /* Brand Colors */
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --primary-light: #3b82f6;
    --secondary: #64748b;
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --info: #06b6d4;
    
    /* Neutral Colors */
    --gray-50: #f8fafc;
    --gray-100: #f1f5f9;
    --gray-200: #e2e8f0;
    --gray-300: #cbd5e1;
    --gray-400: #94a3b8;
    --gray-500: #64748b;
    --gray-600: #475569;
    --gray-700: #334155;
    --gray-800: #1e293b;
    --gray-900: #0f172a;
    
    /* Layout */
    --sidebar-width: 280px;
    --header-height: 70px;
    --border-radius: 8px;
    --border-radius-lg: 12px;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06);
    --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);
    
    /* Transitions */
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-fast: all 0.15s cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'Fira Code', 'Monaco', 'Cascadia Code', monospace;
}

/* Reset & Base */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

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

body {
    font-family: var(--font-family);
    line-height: 1.6;
    color: var(--gray-800);
    background: var(--gray-50);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Loading Screen */
.loading-screen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    color: white;
}

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

.loading-spinner {
    width: 60px;
    height: 60px;
    border: 4px solid rgba(255, 255, 255, 0.2);
    border-top: 4px solid white;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin: 0 auto 20px;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Authentication Screens */
.auth-screen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
}

.auth-container {
    width: 100%;
    max-width: 420px;
    margin: 20px;
    background: white;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-xl);
    overflow: hidden;
}

.auth-header {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    text-align: center;
    padding: 40px 30px;
}

.auth-header .logo {
    font-size: 48px;
    margin-bottom: 20px;
}

.auth-header h1 {
    font-size: 28px;
    font-weight: 700;
    margin-bottom: 10px;
}

.auth-header p {
    opacity: 0.9;
    font-size: 14px;
}

.auth-form {
    padding: 40px 30px;
}

.form-group {
    margin-bottom: 20px;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 15px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--gray-700);
    font-size: 14px;
}

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

.input-group i {
    position: absolute;
    left: 15px;
    color: var(--gray-400);
    z-index: 1;
}

.input-group input,
.input-group select {
    width: 100%;
    padding: 12px 15px 12px 45px;
    border: 2px solid var(--gray-200);
    border-radius: var(--border-radius);
    font-size: 14px;
    transition: var(--transition);
    background: white;
}

.input-group input:focus,
.input-group select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.password-toggle {
    position: absolute;
    right: 15px;
    background: none;
    border: none;
    color: var(--gray-400);
    cursor: pointer;
    padding: 5px;
    border-radius: 4px;
    transition: var(--transition-fast);
}

.password-toggle:hover {
    color: var(--gray-600);
    background: var(--gray-100);
}

.form-options {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 25px;
}

.checkbox-label {
    display: flex;
    align-items: center;
    cursor: pointer;
    font-size: 14px;
    color: var(--gray-600);
}

.checkbox-label input[type="checkbox"] {
    display: none;
}

.checkmark {
    width: 18px;
    height: 18px;
    border: 2px solid var(--gray-300);
    border-radius: 4px;
    margin-right: 8px;
    position: relative;
    transition: var(--transition);
}

.checkbox-label input[type="checkbox"]:checked + .checkmark {
    background: var(--primary);
    border-color: var(--primary);
}

.checkbox-label input[type="checkbox"]:checked + .checkmark::after {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: 12px;
    font-weight: bold;
}

.forgot-password {
    color: var(--primary);
    text-decoration: none;
    font-size: 14px;
    transition: var(--transition-fast);
}

.forgot-password:hover {
    color: var(--primary-dark);
    text-decoration: underline;
}

.auth-footer {
    text-align: center;
    margin-top: 30px;
    padding-top: 20px;
    border-top: 1px solid var(--gray-200);
}

.auth-footer p {
    color: var(--gray-600);
    font-size: 14px;
}

.auth-footer a {
    color: var(--primary);
    text-decoration: none;
    font-weight: 600;
    transition: var(--transition-fast);
}

.auth-footer a:hover {
    color: var(--primary-dark);
    text-decoration: underline;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 24px;
    border: none;
    border-radius: var(--border-radius);
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
    line-height: 1;
}

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

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-full {
    width: 100%;
}

/* Password Strength */
.password-strength {
    margin-top: 8px;
}

.strength-bar {
    height: 4px;
    background: var(--gray-200);
    border-radius: 2px;
    overflow: hidden;
    margin-bottom: 5px;
}

.strength-bar::after {
    content: '';
    display: block;
    height: 100%;
    width: 0;
    transition: var(--transition);
    border-radius: 2px;
}

.strength-text {
    font-size: 12px;
    color: var(--gray-600);
}

.strength-weak .strength-bar::after {
    width: 33%;
    background: var(--danger);
}

.strength-medium .strength-bar::after {
    width: 66%;
    background: var(--warning);
}

.strength-strong .strength-bar::after {
    width: 100%;
    background: var(--success);
}

/* Main Application */
.main-app {
    display: flex;
    height: 100vh;
    background: var(--gray-50);
}

/* Sidebar */
.sidebar {
    width: var(--sidebar-width);
    background: white;
    border-right: 1px solid var(--gray-200);
    display: flex;
    flex-direction: column;
    transition: var(--transition);
    position: relative;
    z-index: 100;
}

.sidebar-header {
    padding: 20px;
    border-bottom: 1px solid var(--gray-200);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.sidebar-header .logo {
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 20px;
    font-weight: 700;
    color: var(--primary);
}

.sidebar-header .logo i {
    font-size: 24px;
}

.sidebar-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--gray-600);
    cursor: pointer;
    padding: 8px;
    border-radius: var(--border-radius);
    transition: var(--transition-fast);
}

.sidebar-toggle:hover {
    background: var(--gray-100);
}

.sidebar-nav {
    flex: 1;
    overflow-y: auto;
    padding: 20px 0;
}

.nav-section {
    margin-bottom: 30px;
}

.nav-section-title {
    font-size: 12px;
    font-weight: 600;
    color: var(--gray-500);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    padding: 0 20px;
    margin-bottom: 10px;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 20px;
    color: var(--gray-700);
    text-decoration: none;
    transition: var(--transition-fast);
    position: relative;
}

.nav-item:hover {
    background: var(--gray-50);
    color: var(--primary);
}

.nav-item.active {
    background: rgba(37, 99, 235, 0.1);
    color: var(--primary);
}

.nav-item.active::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 3px;
    background: var(--primary);
}

.nav-item i {
    width: 20px;
    text-align: center;
}

/* Main Content */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.main-header {
    height: var(--header-height);
    background: white;
    border-bottom: 1px solid var(--gray-200);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 30px;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 20px;
}

.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--gray-600);
    cursor: pointer;
    padding: 8px;
    border-radius: var(--border-radius);
    transition: var(--transition-fast);
}

.mobile-menu-toggle:hover {
    background: var(--gray-100);
}

.main-header h1 {
    font-size: 24px;
    font-weight: 700;
    color: var(--gray-800);
}

.header-right {
    display: flex;
    align-items: center;
}

.user-menu {
    position: relative;
}

.user-avatar {
    display: flex;
    align-items: center;
    gap: 10px;
    background: none;
    border: 1px solid var(--gray-200);
    border-radius: var(--border-radius);
    padding: 8px 15px;
    cursor: pointer;
    transition: var(--transition-fast);
}

.user-avatar:hover {
    background: var(--gray-50);
    border-color: var(--gray-300);
}

.user-avatar i:first-child {
    font-size: 20px;
    color: var(--gray-600);
}

.user-dropdown {
    position: absolute;
    top: 100%;
    right: 0;
    background: white;
    border: 1px solid var(--gray-200);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-lg);
    min-width: 200px;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-10px);
    transition: var(--transition-fast);
}

.user-dropdown.show {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.user-dropdown a {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 12px 15px;
    color: var(--gray-700);
    text-decoration: none;
    transition: var(--transition-fast);
}

.user-dropdown a:hover {
    background: var(--gray-50);
    color: var(--primary);
}

.dropdown-divider {
    height: 1px;
    background: var(--gray-200);
    margin: 5px 0;
}

/* Page Content */
.page-content {
    flex: 1;
    overflow-y: auto;
    padding: 30px;
}

#page-container {
    max-width: 1200px;
    margin: 0 auto;
}

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

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

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

/* Alerts */
.alert-container {
    margin-bottom: 20px;
}

.alert {
    padding: 15px;
    border-radius: var(--border-radius);
    margin-bottom: 10px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.alert-success {
    background: rgba(16, 185, 129, 0.1);
    color: var(--success);
    border: 1px solid rgba(16, 185, 129, 0.2);
}

.alert-error {
    background: rgba(239, 68, 68, 0.1);
    color: var(--danger);
    border: 1px solid rgba(239, 68, 68, 0.2);
}

.alert-warning {
    background: rgba(245, 158, 11, 0.1);
    color: var(--warning);
    border: 1px solid rgba(245, 158, 11, 0.2);
}

/* Notifications */
.notification-container {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 9999;
}

.notification {
    background: white;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-lg);
    padding: 15px 20px;
    margin-bottom: 10px;
    min-width: 300px;
    display: flex;
    align-items: center;
    gap: 12px;
    animation: slideIn 0.3s ease-out;
}

@keyframes slideIn {
    from {
        transform: translateX(100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

.notification.success {
    border-left: 4px solid var(--success);
}

.notification.error {
    border-left: 4px solid var(--danger);
}

.notification.warning {
    border-left: 4px solid var(--warning);
}

.notification.info {
    border-left: 4px solid var(--info);
}

/* Responsive Design */
@media (max-width: 768px) {
    .sidebar {
        position: fixed;
        left: -100%;
        top: 0;
        height: 100vh;
        z-index: 1000;
        box-shadow: var(--shadow-xl);
    }
    
    .sidebar.open {
        left: 0;
    }
    
    .sidebar-toggle,
    .mobile-menu-toggle {
        display: block;
    }
    
    .main-header {
        padding: 0 20px;
    }
    
    .page-content {
        padding: 20px;
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .auth-container {
        margin: 10px;
    }
    
    .auth-form {
        padding: 30px 20px;
    }
}

@media (max-width: 480px) {
    .auth-header {
        padding: 30px 20px;
    }
    
    .auth-header h1 {
        font-size: 24px;
    }
    
    .form-options {
        flex-direction: column;
        gap: 15px;
        align-items: flex-start;
    }
    
    .main-header h1 {
        font-size: 20px;
    }
    
    .user-avatar span {
        display: none;
    }
}