:root {
    --bg-main: #f4f6fb;
    --bg-glass: rgba(255, 255, 255, 0.7);
    --bg-glass-hover: rgba(255, 255, 255, 0.9);
    --border-glass: rgba(255, 255, 255, 0.5);
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --accent: #6366f1;
    --accent-hover: #4f46e5;
    --shadow: 0 8px 32px 0 rgba(31, 38, 135, 0.07);
    --msg-sent: #6366f1;
    --msg-sent-text: white;
    --msg-received: #ffffff;
    --msg-received-text: #1e293b;
    --sidebar-bg: #eceffd;
}

[data-theme="dark"] {
    --bg-main: #0f172a;
    --bg-glass: rgba(30, 41, 59, 0.7);
    --bg-glass-hover: rgba(30, 41, 59, 0.9);
    --border-glass: rgba(255, 255, 255, 0.1);
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent: #818cf8;
    --accent-hover: #6366f1;
    --shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.3);
    --msg-sent: #818cf8;
    --msg-sent-text: white;
    --msg-received: #1e293b;
    --msg-received-text: #f8fafc;
    --sidebar-bg: #1e293b;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Inter', sans-serif;
    transition: background-color 0.3s, color 0.3s;
}

body {
    background: var(--bg-main);
    color: var(--text-primary);
    height: 100vh;
    overflow: hidden;
}

/* Utils */
.hidden { display: none !important; }
.active { display: flex !important; }
.screen {
    width: 100vw;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

/* Glassmorphism */
.glass-panel {
    background: var(--bg-glass);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--border-glass);
    border-radius: 24px;
    box-shadow: var(--shadow);
}

/* Auth Screen */
.auth-panel {
    padding: 40px;
    width: 100%;
    max-width: 400px;
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.logo {
    text-align: center;
    font-size: 2rem;
    color: var(--accent);
    margin-bottom: 10px;
}
.logo h1 { font-weight: 700; font-size: 2rem; display: inline-block; margin-left: 10px; color: var(--text-primary) }

.auth-tabs {
    display: flex;
    background: var(--sidebar-bg);
    border-radius: 12px;
    overflow: hidden;
}
.auth-tabs .tab {
    flex: 1;
    padding: 12px;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-weight: 600;
    cursor: pointer;
}
.auth-tabs .tab.active {
    background: var(--accent);
    color: white;
}

.auth-form {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.input-group {
    position: relative;
    display: flex;
    align-items: center;
}
.input-group i {
    position: absolute;
    left: 16px;
    color: var(--text-secondary);
}
.input-group input, .modern-input {
    width: 100%;
    padding: 14px 16px 14px 45px;
    border-radius: 12px;
    border: 1px solid var(--border-glass);
    background: var(--bg-main);
    color: var(--text-primary);
    font-size: 1rem;
    outline: none;
    transition: all 0.3s;
}
.modern-input { padding: 14px 16px; }
.input-group input:focus, .modern-input:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

.btn-primary {
    background: var(--accent);
    color: white;
    padding: 14px;
    border: none;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s, background 0.3s;
}
.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-2px);
}
.mt-3 { margin-top: 1rem; }

/* App Screen */
.app-container {
    display: flex;
    width: 95vw;
    height: 95vh;
    background: var(--bg-glass);
    backdrop-filter: blur(16px);
    border: 1px solid var(--border-glass);
    border-radius: 24px;
    box-shadow: var(--shadow);
    overflow: hidden;
}

/* Sidebar */
.sidebar {
    width: 320px;
    background: var(--sidebar-bg);
    display: flex;
    flex-direction: column;
    border-right: 1px solid var(--border-glass);
}

.sidebar-header {
    padding: 24px 24px 12px;
}

.profile-card {
    display: flex;
    align-items: center;
    gap: 16px;
    background: var(--bg-glass);
    padding: 12px;
    border-radius: 20px;
    border: 1px solid var(--border-glass);
}

.user-details {
    display: flex;
    flex-direction: column;
}

.user-details span#current-username {
    font-weight: 700;
    font-size: 1.1rem;
    color: var(--text-primary);
}

.status-online {
    font-size: 0.75rem;
    color: #10b981;
    font-weight: 500;
}

.avatar {
    width: 45px;
    height: 45px;
    border-radius: 12px;
    background: var(--accent);
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.3);
}

.sidebar-actions {
    display: flex;
    gap: 8px;
    padding: 0 24px 24px;
    border-bottom: 1px solid var(--border-glass);
}

.btn-action {
    flex: 1;
    background: var(--bg-glass);
    border: 1px solid var(--border-glass);
    color: var(--text-secondary);
    padding: 10px;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.1rem;
}

.btn-action:hover {
    background: var(--accent);
    color: white;
    border-color: var(--accent);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.2);
}

.btn-action.logout:hover {
    background: #ef4444;
    border-color: #ef4444;
    box-shadow: 0 4px 12px rgba(239, 68, 68, 0.2);
}

.btn-icon {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    font-size: 1.2rem;
    cursor: pointer;
    padding: 8px;
    border-radius: 50%;
}
.btn-icon:hover { color: var(--accent); background: var(--bg-glass); }

.sidebar-search { padding: 0 24px 16px; }
.search-bar { position: relative; }
.search-bar i { position: absolute; left: 16px; top: 12px; color: var(--text-secondary); }
.search-bar input {
    width: 100%;
    padding: 10px 16px 10px 40px;
    border-radius: 20px;
    border: none;
    background: var(--bg-main);
    color: var(--text-primary);
    outline: none;
}

.section { padding: 12px 24px; display: flex; flex-direction: column; }
.section h3 {
    font-size: 0.8rem;
    text-transform: uppercase;
    color: var(--text-secondary);
    letter-spacing: 1px;
    margin-bottom: 12px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.badge { background: #ef4444; color: white; padding: 2px 6px; border-radius: 10px; font-size: 0.7rem; }

.list { list-style: none; overflow-y: auto; flex-grow: 1; }
.list li {
    padding: 12px;
    border-radius: 12px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 12px;
    transition: background 0.2s;
}
.list li:hover { background: var(--bg-glass-hover); }
.list li.active { background: var(--bg-glass); border-left: 4px solid var(--accent); }
.list li .name { font-weight: 500; flex-grow: 1; }

.btn-xs { background: transparent; border: none; color: var(--accent); cursor: pointer; }

.btn-delete {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    opacity: 0;
    transition: opacity 0.2s, color 0.2s;
    padding: 4px 8px;
    border-radius: 8px;
    font-size: 0.85rem;
}
.list li:hover .btn-delete { opacity: 1; }
.btn-delete:hover { color: #ef4444; background: rgba(239, 68, 68, 0.1); }

.chat-header { justify-content: space-between; }
.chat-info { display: flex; align-items: center; gap: 12px; flex-grow: 1; }
.delete-conv { color: var(--text-secondary); }
.delete-conv:hover { color: #ef4444; }

/* Chat Area */
.chat-area {
    flex-grow: 1;
    display: flex;
    flex-direction: column;
    background: transparent;
}

.chat-header {
    padding: 24px;
    border-bottom: 1px solid var(--border-glass);
    display: flex;
    align-items: center;
}

.messages-container {
    flex-grow: 1;
    padding: 24px;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.welcome-placeholder {
    margin: auto;
    text-align: center;
    color: var(--text-secondary);
}
.welcome-placeholder i { font-size: 4rem; color: var(--accent); margin-bottom: 16px; opacity: 0.5; }

.message {
    max-width: 65%;
    padding: 12px 16px;
    border-radius: 18px;
    position: relative;
    animation: fadeIn 0.3s ease-out;
}
.message .sender-name { font-size: 0.75rem; opacity: 0.7; margin-bottom: 4px; display: block;}

.message.sent {
    align-self: flex-end;
    background: var(--msg-sent);
    color: var(--msg-sent-text);
    border-bottom-right-radius: 4px;
}
.message.sent .sender-name { display: none; }

.message.received {
    align-self: flex-start;
    background: var(--msg-received);
    color: var(--msg-received-text);
    border-bottom-left-radius: 4px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.message-input-area {
    padding: 20px 24px;
    border-top: 1px solid var(--border-glass);
    display: flex;
    gap: 12px;
}

.message-input-area input {
    flex-grow: 1;
    padding: 16px 24px;
    border-radius: 24px;
    border: none;
    background: var(--bg-main);
    color: var(--text-primary);
    outline: none;
    box-shadow: inset 0 2px 4px rgba(0,0,0,0.05);
}

.message-input-area button {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background: var(--accent);
    color: white;
    display: flex;
    justify-content: center;
    align-items: center;
}

/* Modals */
.modal {
    position: fixed;
    top: 0; left: 0; width: 100vw; height: 100vh;
    background: rgba(0,0,0,0.5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 100;
}
.modal-content {
    background: var(--bg-main);
    padding: 32px;
    border-radius: 24px;
    width: 400px;
    max-width: 90vw;
    position: relative;
    box-shadow: 0 20px 40px rgba(0,0,0,0.2);
}
.close-modal {
    position: absolute;
    top: 16px; right: 24px;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-secondary);
}

.multi-select li { display: flex; justify-content: space-between; }
.add-btn { background: var(--accent); color: white; border: none; padding: 4px 12px; border-radius: 12px; cursor: pointer; }

/* Toast */
#toast-container {
    position: fixed;
    top: 20px;
    right: 20px;
    display: flex;
    flex-direction: column;
    gap: 10px;
    z-index: 1000;
}
.toast {
    background: var(--bg-glass);
    backdrop-filter: blur(10px);
    color: var(--text-primary);
    padding: 16px 24px;
    border-radius: 12px;
    border-left: 4px solid var(--accent);
    box-shadow: var(--shadow);
    animation: slideIn 0.3s ease-out;
}

@keyframes fadeIn { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }
@keyframes slideIn { from { transform: translateX(100%); } to { transform: translateX(0); } }

.message-input-area .attach {
    background: transparent;
    color: var(--text-secondary);
}
.message-input-area .attach:hover {
    color: var(--accent);
    background: var(--bg-glass);
}
.file-message {
    display: flex;
    flex-direction: column;
    gap: 8px;
    align-items: center;
    max-width: 200px;
    text-align: center;
}
.file-message i { font-size: 2rem; }
.file-message a { color: inherit; text-decoration: underline; font-weight: 600; word-break: break-all; font-size: 0.9rem;}
.progress-bar-bg { width: 100%; height: 6px; background: rgba(0,0,0,0.1); border-radius: 3px; overflow: hidden; margin-top: 4px; }
.progress-bar-fill { height: 100%; background: #22c55e; width: 0%; transition: width 0.2s; }

/* Mobile Reponsive Fixes */
.mobile-only { display: none !important; }

@media (max-width: 768px) {
    .mobile-only { display: flex !important; }
    
    .screen {
        height: 100vh;
        height: 100dvh;
        align-items: flex-start; /* Ensure no top gap by aligning to the start */
        justify-content: flex-start;
    }
    
    .app-container {
        width: 100vw;
        height: 100vh;
        height: 100dvh;
        border-radius: 0;
        border: none;
        display: flex;
        flex-direction: row;
        overflow: hidden;
    }
    
    .sidebar {
        position: fixed;
        top: 0;
        left: 0;
        height: 100vh;
        height: 100dvh;
        width: 280px;
        z-index: 1001;
        transform: translateX(-100%);
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        box-shadow: 10px 0 30px rgba(0,0,0,0.2);
    }
    
    .sidebar.sidebar-open {
        transform: translateX(0);
    }
    
    #sidebar-overlay {
        position: fixed;
        top: 0;
        left: 0;
        width: 100vw;
        height: 100vh;
        height: 100dvh;
        background: rgba(0,0,0,0.5);
        backdrop-filter: blur(4px);
        z-index: 1000;
        display: block !important;
        opacity: 0;
        pointer-events: none;
        transition: opacity 0.3s ease;
    }
    
    #sidebar-overlay.overlay-active {
        opacity: 1;
        pointer-events: auto;
    }
    
    .chat-area {
        width: 100%;
        height: 100%;
        display: flex;
        flex-direction: column;
    }
    
    .chat-header {
        padding: 16px;
        gap: 12px;
        flex-shrink: 0;
    }

    .messages-container {
        flex-grow: 1;
        overflow-y: auto;
    }
    
    .message {
        max-width: 85%;
    }
    
    .message-input-area {
        padding: 12px;
        gap: 8px;
        flex-shrink: 0; /* Prevent input area from being squashed or pushed out */
        background: var(--bg-glass);
    }
    
    .message-input-area input {
        padding: 12px 16px;
    }

    .auth-panel {
        padding: 24px;
        margin: 16px;
        max-width: calc(100% - 32px);
    }
}