:root {
    --primary-color: #2196F3;
    --primary-dark: #1976D2;
    --secondary-color: #4CAF50;
    --danger-color: #f44336;
    --bg-color: #f5f5f5;
    --card-bg: #ffffff;
    --text-primary: #212121;
    --text-secondary: #757575;
    --border-color: #e0e0e0;
    --shadow: 0 2px 4px rgba(0,0,0,0.1);
    --shadow-hover: 0 4px 8px rgba(0,0,0,0.15);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
}

.app-container {
    max-width: 800px;
    margin: 0 auto;
    padding-bottom: 60px;
}

/* Header */
.app-header {
    background: var(--primary-color);
    color: white;
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.app-header h1 {
    font-size: 1.5rem;
    font-weight: 500;
}

.install-btn {
    background: white;
    color: var(--primary-color);
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    cursor: pointer;
    font-weight: 500;
    transition: transform 0.2s;
}

.install-btn:hover {
    transform: scale(1.05);
}

/* Tabs */
.tabs {
    display: flex;
    background: white;
    box-shadow: var(--shadow);
}

.tab-btn {
    flex: 1;
    padding: 1rem;
    border: none;
    background: none;
    cursor: pointer;
    font-size: 1rem;
    color: var(--text-secondary);
    border-bottom: 3px solid transparent;
    transition: all 0.3s;
}

.tab-btn.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
    font-weight: 500;
}

.tab-btn:hover {
    background: rgba(33, 150, 243, 0.05);
}

/* Tab Content */
.tab-content {
    display: none;
    padding: 1rem;
    animation: fadeIn 0.3s;
}

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

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

/* Cards */
.card {
    background: var(--card-bg);
    border-radius: 8px;
    padding: 1.5rem;
    margin-bottom: 1rem;
    box-shadow: var(--shadow);
    transition: box-shadow 0.3s;
}

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

.card h2 {
    font-size: 1.25rem;
    margin-bottom: 1rem;
    color: var(--text-primary);
    font-weight: 500;
}

/* Forms */
form {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

input, textarea, select {
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-size: 1rem;
    font-family: inherit;
    transition: border-color 0.3s, box-shadow 0.3s;
}

input:focus, textarea:focus, select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

textarea {
    resize: vertical;
    min-height: 80px;
}

.message-input-wrapper {
    position: relative;
}

.char-counter {
    position: absolute;
    bottom: 0.5rem;
    right: 0.5rem;
    font-size: 0.75rem;
    color: var(--text-secondary);
    background: rgba(255, 255, 255, 0.9);
    padding: 0.25rem 0.5rem;
    border-radius: 4px;
}

/* Buttons */
.btn-primary {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 4px;
    font-size: 1rem;
    cursor: pointer;
    font-weight: 500;
    transition: background 0.3s, transform 0.1s;
}

.btn-primary:hover {
    background: var(--primary-dark);
}

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

.btn-secondary {
    background: var(--secondary-color);
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: opacity 0.3s;
}

.btn-secondary:hover {
    opacity: 0.9;
}

.btn-danger {
    background: var(--danger-color);
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: opacity 0.3s;
}

.btn-danger:hover {
    opacity: 0.9;
}

/* Contact Item */
.contact-item {
    padding: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    margin-bottom: 0.75rem;
    transition: border-color 0.3s, box-shadow 0.3s;
}

.contact-item:hover {
    border-color: var(--primary-color);
    box-shadow: var(--shadow);
}

.contact-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 0.5rem;
}

.contact-name {
    font-weight: 500;
    font-size: 1.1rem;
    color: var(--text-primary);
}

.contact-actions {
    display: flex;
    gap: 0.5rem;
}

.contact-details {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.contact-details div {
    margin-bottom: 0.25rem;
}

/* Messages */
.filter-buttons {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1rem;
}

.filter-btn {
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    background: white;
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.3s;
}

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

.filter-btn:hover:not(.active) {
    background: var(--bg-color);
}

.message-item {
    padding: 1rem;
    border-left: 4px solid var(--primary-color);
    background: var(--bg-color);
    border-radius: 4px;
    margin-bottom: 0.75rem;
}

.message-item.sent {
    border-left-color: var(--secondary-color);
}

.message-item.received {
    border-left-color: var(--primary-color);
}

.message-header {
    display: flex;
    justify-content: space-between;
    margin-bottom: 0.5rem;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.message-recipient {
    font-weight: 500;
}

.message-text {
    color: var(--text-primary);
    word-wrap: break-word;
    line-height: 1.5;
}

.message-footer {
    margin-top: 0.5rem;
    display: flex;
    justify-content: flex-end;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 2rem;
    color: var(--text-secondary);
}

.empty-state::before {
    content: '📭';
    display: block;
    font-size: 3rem;
    margin-bottom: 0.5rem;
}

/* Status Bar */
.status-bar {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    padding: 0.75rem;
    background: var(--secondary-color);
    color: white;
    text-align: center;
    transform: translateY(100%);
    transition: transform 0.3s;
    z-index: 1000;
}

.status-bar.show {
    transform: translateY(0);
}

.status-bar.error {
    background: var(--danger-color);
}

/* Responsive Design */
@media (max-width: 600px) {
    .app-header h1 {
        font-size: 1.25rem;
    }

    .install-btn {
        padding: 0.4rem 0.8rem;
        font-size: 0.9rem;
    }

    .card {
        padding: 1rem;
    }

    .contact-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
    }

    .filter-buttons {
        flex-wrap: wrap;
    }
}

/* Loading State */
.loading {
    text-align: center;
    padding: 2rem;
    color: var(--text-secondary);
}

.loading::after {
    content: '...';
    animation: dots 1.5s steps(4, end) infinite;
}

@keyframes dots {
    0%, 20% { content: '.'; }
    40% { content: '..'; }
    60%, 100% { content: '...'; }
}