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

:root {
    --primary-color: #007bff;
    --secondary-color: #6c757d;
    --bg-primary: #ffffff;
    --bg-secondary: #f8f9fa;
    --bg-tertiary: #e9ecef;
    --text-primary: #212529;
    --text-secondary: #6c757d;
    --border-color: #dee2e6;
    --success-color: #28a745;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 4px 12px rgba(0, 0, 0, 0.15);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: var(--bg-secondary);
    color: var(--text-primary);
    overflow: hidden;
}

.screen {
    display: none;
    width: 100%;
    height: 100vh;
    position: absolute;
    top: 0;
    left: 0;
}

.screen.active {
    display: flex;
}

/* Login Screen */
.login-container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, var(--primary-color) 0%, #0056b3 100%);
    color: white;
}

.login-container h1 {
    font-size: 2.5rem;
    margin-bottom: 2rem;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

#loginForm {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: var(--shadow-lg);
    width: 90%;
    max-width: 400px;
    color: var(--text-primary);
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--text-primary);
}

.form-group input[type="text"] {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    font-size: 1rem;
}

.form-group input[type="text"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.1);
}

.avatar-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 0.75rem;
}

.avatar-grid input[type="radio"] {
    display: none;
}

.avatar-grid label {
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 2rem;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
    margin: 0;
}

.avatar-grid input[type="radio"]:checked + label {
    border-color: var(--primary-color);
    background: rgba(0, 123, 255, 0.1);
    transform: scale(1.1);
}

.avatar-grid label:hover {
    border-color: var(--primary-color);
}

/* Buttons */
.btn {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 5px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
}

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

.btn-primary:hover {
    background: #0056b3;
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-small {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
    background: var(--bg-tertiary);
    color: var(--text-primary);
    margin-top: 0.5rem;
    width: 100%;
}

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

.btn-send {
    background: var(--primary-color);
    color: white;
    padding: 0.75rem 1.5rem;
}

.btn-send:hover:not(:disabled) {
    background: #0056b3;
}

.btn-send:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Chat Container */
.chat-container {
    display: flex;
    height: 100vh;
    background: var(--bg-primary);
}

/* Sidebar */
.sidebar {
    width: 280px;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
}

.user-profile {
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    gap: 0.75rem;
    align-items: flex-start;
}

.user-avatar {
    font-size: 2.5rem;
    flex-shrink: 0;
}

.user-info {
    flex: 1;
}

.username {
    font-weight: 600;
    margin-bottom: 0.25rem;
}

/* Chat Rooms */
.chat-rooms,
.direct-messages {
    padding: 1rem;
    flex: 1;
    overflow-y: auto;
}

.chat-rooms h3,
.direct-messages h3 {
    font-size: 0.875rem;
    text-transform: uppercase;
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
    font-weight: 700;
}

.rooms-list,
.dm-list {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.room-item,
.dm-item {
    padding: 0.75rem 1rem;
    border-radius: 5px;
    cursor: pointer;
    transition: all 0.2s;
    color: var(--text-secondary);
    user-select: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.room-item:hover,
.dm-item:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.room-item.active,
.dm-item.active {
    background: var(--primary-color);
    color: white;
}

.dm-item {
    font-size: 0.95rem;
}

.dm-avatar {
    font-size: 1.25rem;
    flex-shrink: 0;
}

/* Main Chat Area */
.chat-main {
    flex: 1;
    display: flex;
    flex-direction: column;
}

.chat-header {
    padding: 1rem 1.5rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.header-content h2 {
    font-size: 1.25rem;
    margin-bottom: 0.25rem;
}

.subtitle {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.online-users {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.online-count {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.online-dot {
    width: 8px;
    height: 8px;
    background: var(--success-color);
    border-radius: 50%;
}

/* Messages Container */
.messages-container {
    flex: 1;
    overflow-y: auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.welcome-message {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100%;
    color: var(--text-secondary);
    text-align: center;
}

.welcome-message h3 {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
}

.message {
    display: flex;
    gap: 0.75rem;
    animation: slideIn 0.3s ease;
}

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

.message-avatar {
    font-size: 2rem;
    flex-shrink: 0;
}

.message-content {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.message-header {
    display: flex;
    gap: 0.5rem;
    align-items: baseline;
}

.message-author {
    font-weight: 600;
    color: var(--text-primary);
}

.message-time {
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.message-text {
    color: var(--text-primary);
    word-wrap: break-word;
    max-width: 500px;
    line-height: 1.4;
}

.message-text.system {
    font-style: italic;
    color: var(--text-secondary);
}

.message.own .message-text {
    background: var(--primary-color);
    color: white;
    padding: 0.5rem 0.75rem;
    border-radius: 8px;
    max-width: fit-content;
}

/* Input Area */
.chat-input-area {
    padding: 1rem 1.5rem;
    border-top: 1px solid var(--border-color);
    background: var(--bg-primary);
}

#messageForm {
    display: flex;
    gap: 0.75rem;
}

#messageInput {
    flex: 1;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: 20px;
    font-size: 1rem;
    resize: none;
    max-height: 100px;
}

#messageInput:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.1);
}

#messageInput:disabled {
    background: var(--bg-tertiary);
    color: var(--text-secondary);
}

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

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

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

::-webkit-scrollbar-thumb:hover {
    background: var(--secondary-color);
}

/* Responsive */
@media (max-width: 768px) {
    .sidebar {
        width: 200px;
    }

    .message-text {
        max-width: 300px;
    }

    .chat-header {
        padding: 0.75rem 1rem;
    }

    .messages-container {
        padding: 1rem;
        gap: 0.75rem;
    }
}