:root {
  --bg: #fafaf9;
  --surface: #ffffff;
  --ink: #0a0a0a;
  --muted: #78716c;
  --faint: #a8a29e;
  --hairline: #e7e5e4;
  --hairline-strong: #d6d3d1;
  --bubble-mine: #0a0a0a;
  --bubble-mine-ink: #fafaf9;
  --bubble-theirs: #f5f5f4;
  --accent: #0a0a0a;
  --danger: #b91c1c;
  --danger-bg: #fef2f2;
  --danger-border: #fecaca;
  --radius: 10px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "Inter", system-ui, sans-serif;
}

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

html, body {
  height: 100%;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 15px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

.screen { height: 100dvh; display: flex; flex-direction: column; }
.screen[hidden] { display: none; }

/* ---------- Auth ---------- */
#auth-screen {
  align-items: center;
  justify-content: center;
  padding: 24px;
}

.auth-card {
  width: 100%;
  max-width: 360px;
  text-align: center;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
}

.brand-mark {
  width: 20px;
  height: 20px;
  border-radius: 5px;
  background: var(--ink);
  position: relative;
  flex-shrink: 0;
}
.brand-mark::after {
  content: "";
  position: absolute;
  inset: 4px;
  border-radius: 2px;
  border: 1.5px solid var(--bg);
  border-right-color: transparent;
  border-bottom-color: transparent;
}

#auth-screen h1 {
  font-size: 20px;
  font-weight: 600;
  letter-spacing: -0.02em;
}

.auth-sub {
  margin-top: 28px;
  margin-bottom: 32px;
  color: var(--muted);
  font-size: 14px;
}

.btn-primary {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  width: 100%;
  padding: 12px 20px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  font-family: inherit;
  font-size: 14px;
  font-weight: 500;
  letter-spacing: -0.01em;
  cursor: pointer;
  transition: opacity 0.15s ease, transform 0.05s ease;
}
.btn-primary:hover { opacity: 0.88; }
.btn-primary:active { transform: scale(0.99); }
.btn-primary:disabled { opacity: 0.5; cursor: not-allowed; }

.auth-error {
  margin-top: 20px;
  font-size: 13px;
  color: var(--danger);
  text-align: left;
  padding: 10px 12px;
  background: var(--danger-bg);
  border: 1px solid var(--danger-border);
  border-radius: 8px;
}

/* ---------- Chat ---------- */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 20px;
  border-bottom: 1px solid var(--hairline);
  background: var(--bg);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand-name {
  font-size: 15px;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.btn-ghost {
  background: transparent;
  border: 1px solid var(--hairline-strong);
  color: var(--ink);
  font-family: inherit;
  font-size: 13px;
  padding: 6px 12px;
  border-radius: 7px;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease;
}
.btn-ghost:hover { background: var(--bubble-theirs); border-color: var(--faint); }

.messages {
  flex: 1;
  overflow-y: auto;
  padding: 20px 20px 8px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.messages::-webkit-scrollbar { width: 8px; }
.messages::-webkit-scrollbar-thumb { background: var(--hairline-strong); border-radius: 8px; }

.msg-group { display: flex; flex-direction: column; gap: 2px; margin-bottom: 14px; }
.msg-group.mine { align-items: flex-end; }
.msg-group.theirs { align-items: flex-start; }

.msg-author {
  font-size: 12px;
  font-weight: 500;
  color: var(--muted);
  margin-bottom: 4px;
  padding: 0 4px;
  letter-spacing: -0.005em;
}

.bubble {
  max-width: min(72%, 560px);
  padding: 9px 14px;
  border-radius: 16px;
  font-size: 14.5px;
  line-height: 1.45;
  word-wrap: break-word;
  overflow-wrap: anywhere;
  white-space: pre-wrap;
  animation: bubble-in 0.18s ease-out;
}

@keyframes bubble-in {
  from { opacity: 0; transform: translateY(4px); }
  to   { opacity: 1; transform: translateY(0); }
}

.mine .bubble {
  background: var(--bubble-mine);
  color: var(--bubble-mine-ink);
  border-bottom-right-radius: 6px;
}

.theirs .bubble {
  background: var(--bubble-theirs);
  color: var(--ink);
  border-bottom-left-radius: 6px;
}

.msg-time {
  font-size: 11px;
  color: var(--faint);
  padding: 2px 4px 0;
}

.empty {
  margin: auto;
  text-align: center;
  color: var(--faint);
  font-size: 14px;
  padding: 40px 20px;
}
.empty strong { display: block; color: var(--ink); font-size: 15px; margin-bottom: 4px; font-weight: 600; }

.send-error {
  margin: 0 20px 8px;
  font-size: 13px;
  color: var(--danger);
  padding: 8px 12px;
  background: var(--danger-bg);
  border: 1px solid var(--danger-border);
  border-radius: 8px;
}

/* ---------- Composer ---------- */
.composer {
  padding: 12px 20px 20px;
  border-top: 1px solid var(--hairline);
  background: var(--bg);
}

.composer-inner {
  display: flex;
  align-items: flex-end;
  gap: 8px;
  background: var(--surface);
  border: 1px solid var(--hairline-strong);
  border-radius: 14px;
  padding: 6px 6px 6px 14px;
  transition: border-color 0.15s ease;
}
.composer-inner:focus-within { border-color: var(--ink); }

#composer-input {
  flex: 1;
  border: none;
  outline: none;
  background: transparent;
  resize: none;
  font-family: inherit;
  font-size: 15px;
  line-height: 1.45;
  color: var(--ink);
  padding: 8px 0;
  max-height: 160px;
}
#composer-input::placeholder { color: var(--faint); }

.btn-send {
  flex-shrink: 0;
  width: 34px;
  height: 34px;
  border-radius: 10px;
  border: none;
  background: var(--ink);
  color: #fff;
  display: grid;
  place-items: center;
  cursor: pointer;
  transition: opacity 0.15s ease, transform 0.05s ease;
}
.btn-send:disabled { opacity: 0.25; cursor: not-allowed; }
.btn-send:not(:disabled):hover { opacity: 0.85; }
.btn-send:not(:disabled):active { transform: scale(0.95); }

@media (max-width: 480px) {
  .messages { padding: 14px 14px 4px; }
  .composer { padding: 10px 14px 14px; }
  .topbar { padding: 12px 14px; }
  .bubble { max-width: 82%; }
  .send-error { margin: 0 14px 8px; }
}