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

:root {
  --bg: #0f1117;
  --bg-2: #1a1d27;
  --bg-3: #22263a;
  --border: #2e3248;
  --accent: #5865f2;
  --accent-hover: #4752c4;
  --text: #e2e4f0;
  --text-muted: #7b82a4;
  --danger: #ed4245;
  --radius: 12px;
  --sidebar-w: 260px;
}

html, body {
  height: 100%;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 15px;
}

/* ── Screens ── */
.screen {
  display: none;
  height: 100vh;
}
.screen.active {
  display: flex;
}

/* ── Login ── */
#login-screen {
  align-items: center;
  justify-content: center;
  background: radial-gradient(ellipse at 50% 0%, #1e2240 0%, var(--bg) 70%);
}

.login-card {
  background: var(--bg-2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 48px 40px;
  width: 100%;
  max-width: 380px;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.login-logo {
  color: var(--accent);
  margin-bottom: 4px;
}

.login-card h1 {
  font-size: 1.8rem;
  font-weight: 700;
  letter-spacing: -0.5px;
}

.login-card > p {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.btn-google {
  display: flex;
  align-items: center;
  gap: 12px;
  background: #fff;
  color: #1a1a2e;
  border: none;
  border-radius: 8px;
  padding: 12px 24px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  width: 100%;
  justify-content: center;
  margin-top: 8px;
  transition: background 0.15s, transform 0.1s;
}
.btn-google:hover { background: #f0f0f0; }
.btn-google:active { transform: scale(0.98); }

.error-msg {
  color: var(--danger);
  font-size: 0.875rem;
}

/* ── Chat Layout ── */
#chat-screen {
  flex-direction: row;
  overflow: hidden;
}

/* ── Sidebar ── */
.sidebar {
  width: var(--sidebar-w);
  flex-shrink: 0;
  background: var(--bg-2);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px 16px;
  border-bottom: 1px solid var(--border);
}

.sidebar-title {
  font-weight: 700;
  font-size: 1rem;
  letter-spacing: -0.3px;
}

.btn-icon {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 6px;
  border-radius: 6px;
  display: flex;
  align-items: center;
  transition: color 0.15s, background 0.15s;
}
.btn-icon:hover {
  color: var(--danger);
  background: rgba(237, 66, 69, 0.12);
}

.current-user {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 16px;
  border-bottom: 1px solid var(--border);
}

.avatar {
  width: 34px;
  height: 34px;
  border-radius: 50%;
  object-fit: cover;
  background: var(--bg-3);
  flex-shrink: 0;
}

#sidebar-name {
  font-size: 0.875rem;
  font-weight: 600;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.sidebar-section-label {
  padding: 16px 16px 6px;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
}

#users-list {
  list-style: none;
  overflow-y: auto;
  flex: 1;
  padding: 4px 8px 8px;
}

#users-list li {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 8px;
  border-radius: 8px;
  font-size: 0.875rem;
}

#users-list li img {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  object-fit: cover;
  background: var(--bg-3);
}

#users-list li span {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  color: var(--text-muted);
}

/* ── Main Chat ── */
.chat-main {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background: var(--bg);
}

.chat-header {
  padding: 16px 24px;
  border-bottom: 1px solid var(--border);
  font-weight: 700;
  font-size: 1rem;
  color: var(--text-muted);
  background: var(--bg);
}

.chat-header-title {
  color: var(--text);
}

.messages-container {
  flex: 1;
  overflow-y: auto;
  padding: 16px 0 8px;
  scroll-behavior: smooth;
}

#messages-list {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

/* ── Messages ── */
.msg {
  display: flex;
  gap: 12px;
  padding: 4px 24px;
  border-radius: 4px;
  transition: background 0.1s;
}
.msg:hover { background: var(--bg-2); }

.msg.grouped { padding-top: 1px; }
.msg.grouped .msg-avatar-col { visibility: hidden; }

.msg-avatar-col {
  flex-shrink: 0;
  width: 38px;
  display: flex;
  align-items: flex-start;
  padding-top: 2px;
}

.msg .avatar {
  width: 38px;
  height: 38px;
}

.msg-body { flex: 1; min-width: 0; }

.msg-header {
  display: flex;
  align-items: baseline;
  gap: 8px;
  margin-bottom: 2px;
}

.msg-author {
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--text);
}

.msg-time {
  font-size: 0.72rem;
  color: var(--text-muted);
}

.msg-text {
  font-size: 0.9375rem;
  line-height: 1.5;
  color: var(--text);
  word-break: break-word;
  white-space: pre-wrap;
}

/* ── Message Form ── */
.message-form {
  display: flex;
  gap: 10px;
  padding: 16px 24px;
  background: var(--bg);
  border-top: 1px solid var(--border);
}

#message-input {
  flex: 1;
  background: var(--bg-3);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 16px;
  color: var(--text);
  font-size: 0.9375rem;
  font-family: inherit;
  outline: none;
  transition: border-color 0.15s;
}
#message-input:focus { border-color: var(--accent); }
#message-input::placeholder { color: var(--text-muted); }

.btn-send {
  background: var(--accent);
  border: none;
  border-radius: 10px;
  width: 46px;
  height: 46px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  cursor: pointer;
  flex-shrink: 0;
  transition: background 0.15s, transform 0.1s;
}
.btn-send:hover { background: var(--accent-hover); }
.btn-send:active { transform: scale(0.95); }
.btn-send:disabled { opacity: 0.5; cursor: default; }

/* ── Date Divider ── */
.date-divider {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 24px;
  color: var(--text-muted);
  font-size: 0.75rem;
  font-weight: 600;
}
.date-divider::before,
.date-divider::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--border);
}

/* ── Utility ── */
.hidden { display: none !important; }

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

/* ── Responsive ── */
@media (max-width: 600px) {
  .sidebar { width: 200px; }
  .msg { padding: 4px 12px; }
  .message-form { padding: 12px; }
}