:root {
    --bg-color: #131314;
    --sidebar-color: #1e1f20;
    --chat-area-color: #131314;
    --user-msg-color: #383a3f;
    --assistant-msg-color: #252629;
    --text-color: #e3e3e3;
    --border-color: #333;
    --accent-color: #4CAF50;
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    height: 100vh;
    overflow: hidden;
}

.app-container {
    display: flex;
    width: 100%;
    height: 100%;
    position: relative;
}

/* Sidebar (hidden on mobile by default) */
.sidebar {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    width: 260px;
    background-color: var(--sidebar-color);
    display: flex;
    flex-direction: column;
    padding: 10px;
    transform: translateX(-100%);
    transition: transform 0.3s ease-in-out;
    z-index: 101; /* Must be on top */
}
.app-container.sidebar-visible .sidebar {
    transform: translateX(0);
}
.sidebar-header {
    display: flex;
    gap: 10px;
    align-items: center;
}
.sidebar-button {
    flex-grow: 1; /* Allow button to take available space */
    padding: 10px 15px;
    background-color: transparent;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    color: var(--text-color);
    cursor: pointer;
    font-size: 1rem;
    display: flex;
    align-items: center;
    gap: 10px;
    transition: background-color 0.2s;
}
.sidebar-button:hover { background-color: var(--user-msg-color); }
.chat-history { flex-grow: 1; overflow-y: auto; margin-top: 20px; }

.chat-history-item {
    padding: 10px 15px;
    margin-bottom: 5px;
    border-radius: 6px;
    cursor: pointer;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    transition: background-color 0.2s;
}
.chat-history-item:hover { background-color: var(--user-msg-color); }
.chat-history-item.active { background-color: var(--user-msg-color); font-weight: bold; }

.close-sidebar-btn {
    background: none;
    border: none;
    color: #999;
    cursor: pointer;
    display: none; /* Hidden by default */
    padding: 5px;
}
.app-container.sidebar-visible .close-sidebar-btn {
    display: block; /* Show when sidebar is visible */
}

/* Main Chat Area */
.chat-area {
    width: 100%;
    display: flex;
    flex-direction: column;
    background-color: var(--chat-area-color);
    position: relative;
    transition: filter 0.3s;
}
.app-container.sidebar-visible .chat-area::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 100;
}

.chat-header { display: flex; align-items: center; padding: 10px; border-bottom: 1px solid var(--border-color); }
.menu-toggle { background: none; border: none; color: var(--text-color); cursor: pointer; }
#chat-title { margin-left: 15px; font-size: 1.1rem; }

.chat-messages { flex-grow: 1; overflow-y: auto; padding: 10px 20px; display: flex; flex-direction: column; }
.welcome-message { text-align: center; margin: auto; color: #888; }

.message { max-width: 90%; margin-bottom: 15px; padding: 10px 15px; border-radius: 12px; line-height: 1.6; word-wrap: break-word; }
.message p, .message ul, .message ol { margin: 0.5em 0; }
.message ul, .message ol { padding-left: 20px; }
.message code { background-color: #111; padding: 2px 4px; border-radius: 4px; }
.message pre { background-color: #111; padding: 10px; border-radius: 8px; overflow-x: auto; }
.message img.user-upload { max-width: 150px; border-radius: 8px; margin-top: 10px; }

.user-message { background-color: var(--user-msg-color); align-self: flex-end; }
.assistant-message { background-color: var(--assistant-msg-color); align-self: flex-start; }
.assistant-message.loading::after { content: '...'; display: inline-block; animation: blink 1s infinite; }
@keyframes blink { 50% { opacity: 0; } }

/* Chat Input */
.chat-input-area { padding: 10px 20px; border-top: 1px solid var(--border-color); }
.image-preview { position: relative; width: 80px; margin-bottom: 10px; }
#image-preview { width: 100%; border-radius: 8px; }
#remove-image-btn {
    position: absolute; top: -5px; right: -5px;
    background: #000; color: #fff; border: 1px solid #fff;
    border-radius: 50%; width: 20px; height: 20px;
    cursor: pointer; display: flex; align-items: center; justify-content: center;
}

.chat-input-wrapper { display: flex; align-items: flex-end; gap: 10px; }
#message-input {
    flex-grow: 1; background: var(--assistant-msg-color);
    border: 1px solid var(--border-color); color: var(--text-color);
    font-size: 1rem; padding: 10px; resize: none;
    max-height: 150px; overflow-y: auto; outline: none; border-radius: 8px;
}

.input-action-btn { background: transparent; border: none; color: #888; cursor: pointer; height: 44px; width: 44px; display: flex; align-items: center; justify-content: center; }
.send-btn { background: var(--accent-color); color: white; border-radius: 8px; }

/* Desktop styles */
@media (min-width: 768px) {
    .chat-header { display: none; }
    .sidebar { position: static; transform: translateX(0); border-right: 1px solid var(--border-color); }
    .close-sidebar-btn { display: none !important; } /* Close button is never needed on desktop */
    .app-container.sidebar-visible .chat-area::before { display: none; } /* No overlay on desktop */
    .chat-area { width: auto; flex-grow: 1; }
}