/* ============================
   CSS Variables & Design System
   ============================ */
:root {
    /* Colors */
    --color-primary: #4f46e5;
    --color-primary-hover: #4338ca;
    --color-success: #10b981;
    --color-warning: #f59e0b;
    --color-danger: #ef4444;
    
    /* Backgrounds */
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    
    /* Text */
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    
    /* Borders */
    --border-color: #e2e8f0;
    --border-radius: 12px;
    --border-radius-sm: 8px;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px 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', system-ui, -apple-system, sans-serif;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.5rem;
    --font-size-2xl: 2rem;
}

/* ============================
   Reset & Base Styles
   ============================ */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

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

/* ============================
   Layout
   ============================ */
.container {
    max-width: 600px;
    margin: 0 auto;
    padding: var(--spacing-lg);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ============================
   Header
   ============================ */
.header {
    text-align: center;
    padding: var(--spacing-xl) 0;
}

.header h1 {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.subtitle {
    color: var(--text-secondary);
    font-size: var(--font-size-base);
}

/* ============================
   Main Content
   ============================ */
.main-content {
    flex: 1;
}

.section {
    background: var(--bg-primary);
    border-radius: var(--border-radius);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
}

.section h2 {
    font-size: var(--font-size-lg);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.divider {
    border: none;
    border-top: 1px solid var(--border-color);
    margin: var(--spacing-xl) 0;
}

/* ============================
   Forms
   ============================ */
.form-group {
    margin-bottom: var(--spacing-md);
}

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

.form-group input,
.form-group textarea {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: var(--font-size-base);
    font-family: var(--font-family);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    background: var(--bg-primary);
    color: var(--text-primary);
    transition: border-color 0.2s, box-shadow 0.2s;
}

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

.form-group input::placeholder,
.form-group textarea::placeholder {
    color: var(--text-muted);
}

/* ============================
   Buttons
   ============================ */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: var(--font-size-base);
    font-weight: 500;
    font-family: var(--font-family);
    border: none;
    border-radius: var(--border-radius-sm);
    cursor: pointer;
    transition: all 0.2s;
}

.btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.btn-primary {
    width: 100%;
    background: var(--color-primary);
    color: white;
}

.btn-primary:hover:not(:disabled) {
    background: var(--color-primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-sm {
    padding: var(--spacing-xs) var(--spacing-sm);
    font-size: var(--font-size-sm);
}

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

.btn-success:hover:not(:disabled) {
    background: #059669;
    transform: translateY(-1px);
}

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

.btn-secondary:hover:not(:disabled) {
    background: var(--border-color);
}

/* ============================
   Item Cards
   ============================ */
.items-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.item-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    padding: var(--spacing-md);
    transition: box-shadow 0.2s, opacity 0.2s;
}

.item-card:hover {
    box-shadow: var(--shadow-md);
}

.item-card.item-returned {
    opacity: 0.7;
    background: var(--bg-tertiary);
}

.item-card.item-returned .item-name {
    text-decoration: line-through;
    color: var(--text-secondary);
}

.item-card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-sm);
}

.item-name {
    font-weight: 600;
    font-size: var(--font-size-base);
    color: var(--text-primary);
}

.item-details {
    font-size: var(--font-size-sm);
    color: var(--text-secondary);
}

.item-details span {
    display: block;
    margin-bottom: var(--spacing-xs);
}

.item-notes {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    font-style: italic;
    margin-top: var(--spacing-sm);
    padding-top: var(--spacing-sm);
    border-top: 1px dashed var(--border-color);
}

.item-actions {
    margin-top: var(--spacing-md);
    padding-top: var(--spacing-sm);
    border-top: 1px solid var(--border-color);
}

/* Status Badges */
.status-badge {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 999px;
    font-size: var(--font-size-sm);
    font-weight: 500;
    flex-shrink: 0;
}

.status-borrowed {
    background: #fef3c7;
    color: #92400e;
}

.status-returned {
    background: #d1fae5;
    color: #065f46;
}

/* ============================
   States
   ============================ */
.empty-state,
.loading {
    text-align: center;
    padding: var(--spacing-xl);
    color: var(--text-muted);
}

.loading {
    animation: pulse 1.5s infinite;
}

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

/* ============================
   Messages
   ============================ */
.message {
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--border-radius-sm);
    margin-bottom: var(--spacing-md);
    font-size: var(--font-size-sm);
    text-align: center;
    animation: slideIn 0.3s ease;
}

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

.message-success {
    background: #d1fae5;
    color: #065f46;
    border: 1px solid #a7f3d0;
}

.message-error {
    background: #fee2e2;
    color: #991b1b;
    border: 1px solid #fecaca;
}

.message-info {
    background: #e0e7ff;
    color: #3730a3;
    border: 1px solid #c7d2fe;
}

/* ============================
   Connection Status
   ============================ */
.connection-status {
    display: inline-block;
    font-size: var(--font-size-sm);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--border-radius-sm);
    margin-top: var(--spacing-sm);
}

.connection-status.connected {
    background: #d1fae5;
    color: #065f46;
}

.connection-status.offline {
    background: #fef3c7;
    color: #92400e;
}

/* ============================
   Item Cards
   ============================ */
.items-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.item-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    padding: var(--spacing-md);
    transition: box-shadow 0.2s;
}

.item-card:hover {
    box-shadow: var(--shadow-md);
}

.item-card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-sm);
}

.item-name {
    font-weight: 600;
    font-size: var(--font-size-base);
    color: var(--text-primary);
}

.item-details {
    font-size: var(--font-size-sm);
    color: var(--text-secondary);
}

.item-details span {
    display: block;
    margin-bottom: var(--spacing-xs);
}

.item-notes {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    font-style: italic;
    margin-top: var(--spacing-sm);
    padding-top: var(--spacing-sm);
    border-top: 1px dashed var(--border-color);
}

/* Status Badges */
.status-badge {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: 999px;
    font-size: var(--font-size-sm);
    font-weight: 500;
}

.status-borrowed {
    background: #fef3c7;
    color: #92400e;
}

.status-returned {
    background: #d1fae5;
    color: #065f46;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: var(--spacing-xl);
    color: var(--text-muted);
}

/* ============================
   Footer
   ============================ */
.footer {
    text-align: center;
    padding: var(--spacing-xl) 0 var(--spacing-md);
    color: var(--text-muted);
    font-size: var(--font-size-sm);
}

/* ============================
   Responsive Design
   ============================ */
@media (max-width: 640px) {
    .container {
        padding: var(--spacing-md);
    }
    
    .header h1 {
        font-size: var(--font-size-xl);
    }
    
    .section {
        padding: var(--spacing-md);
    }
}