:root {
  --bg: linear-gradient(180deg, #eef5ff 0%, #f7f9fc 100%);
  --surface: #ffffff;
  --surface-2: #f8fafc;
  --surface-3: #eef4ff;
  --border: #e5e7eb;
  --text: #1f2937;
  --muted: #64748b;
  --primary: #2563eb;
  --primary-2: #3b82f6;
  --success: #10b981;
  --shadow: rgba(15, 23, 42, 0.08);
}

body.dark {
  --bg: linear-gradient(180deg, #0f172a 0%, #111827 100%);
  --surface: #0f172a;
  --surface-2: #0b1220;
  --surface-3: #172554;
  --border: #334155;
  --text: #e5eefb;
  --muted: #94a3b8;
  --primary: #60a5fa;
  --primary-2: #3b82f6;
  --success: #22c55e;
  --shadow: rgba(0, 0, 0, 0.45);
}

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

body {
  font-family: 'Microsoft YaHei', sans-serif;
  background: var(--bg);
  color: var(--text);
}

button,
input,
select {
  font: inherit;
}

button {
  cursor: pointer;
}

body.dark input,
body.dark select,
body.dark button {
  color: var(--text);
}

.app-shell {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
}

.auth-panel {
  width: min(420px, 100%);
}

.auth-card {
  background: var(--surface);
  border-radius: 18px;
  padding: 32px 24px;
  box-shadow: 0 20px 45px var(--shadow);
}

.auth-card h2 {
  text-align: center;
  margin-bottom: 20px;
  font-size: 1.6rem;
}

.input-group {
  margin-bottom: 14px;
}

.input-group label {
  display: block;
  font-size: 0.92rem;
  margin-bottom: 6px;
  color: var(--muted);
}

.input-group input,
.input-group select {
  width: 100%;
  padding: 12px 14px;
  border-radius: 10px;
  border: 1px solid var(--border);
  outline: none;
  background: var(--surface);
  transition: border-color 0.2s;
}

.input-group input:focus,
.input-group select:focus {
  border-color: var(--primary);
}

.auth-actions {
  display: flex;
  gap: 10px;
  margin-top: 18px;
}

.auth-actions button,
.search-box button,
.chat-input-area button,
.logout-btn,
.theme-btn,
.file-btn,
.group-btn,
.search-result button,
.friend-item,
.group-modal button,
.group-invite-row button,
.save-group-btn,
.group-manage-btn {
  transition: transform 0.15s ease, background 0.2s ease;
}

.auth-actions button {
  flex: 1;
  padding: 11px 12px;
  border: none;
  border-radius: 10px;
  color: #fff;
  background: linear-gradient(90deg, var(--primary), var(--primary-2));
}

.auth-actions button:hover,
.search-box button:hover,
.chat-input-area button:hover,
.logout-btn:hover,
.theme-btn:hover,
.file-btn:hover,
.group-btn:hover,
.search-result button:hover,
.friend-item:hover,
.group-modal button:hover,
.group-invite-row button:hover,
.save-group-btn:hover,
.group-manage-btn:hover {
  transform: translateY(-1px);
}

.chat-container {
  width: min(1100px, 100%);
  height: 88vh;
  display: grid;
  grid-template-columns: 320px 1fr;
  background: var(--surface);
  border-radius: 18px;
  overflow: hidden;
  box-shadow: 0 20px 45px var(--shadow);
}

.sidebar {
  background: var(--surface-2);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
}

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

.avatar,
.friend-avatar {
  width: 48px;
  height: 48px;
  display: grid;
  place-items: center;
  background: var(--surface-3);
  border-radius: 50%;
  font-size: 1.3rem;
}

.info {
  flex: 1;
}

.nickname {
  font-weight: 600;
}

.status {
  font-size: 0.88rem;
  color: var(--muted);
}

.logout-btn,
.theme-btn {
  width: 40px;
  height: 40px;
  background: var(--surface-3);
  border: none;
  border-radius: 50%;
  color: var(--primary);
}

.search-box {
  display: flex;
  gap: 8px;
  padding: 14px;
}

.group-btn {
  padding: 0 10px;
  background: var(--surface-3);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--primary);
}

.search-box input {
  flex: 1;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  outline: none;
  background: var(--surface);
}

.search-box button {
  width: 44px;
  background: var(--primary);
  border: none;
  color: #fff;
  border-radius: 10px;
}

.friend-list {
  flex: 1;
  overflow-y: auto;
  padding: 8px;
}

.friend-item {
  width: 100%;
  display: flex;
  align-items: center;
  gap: 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px;
  margin-bottom: 8px;
}

.friend-item.group-chat-item {
  background: linear-gradient(90deg, var(--surface-3), var(--surface));
}

.friend-info {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}

.chat-main {
  display: flex;
  flex-direction: column;
  background: var(--surface);
}

.chat-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 18px;
  border-bottom: 1px solid var(--border);
  font-weight: 600;
}

.chat-header .chat-user-info {
  display: flex;
  flex-direction: column;
}

.group-manage-btn {
  background: var(--surface-3);
  color: var(--primary);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 8px 10px;
}

.chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: 18px;
  background: linear-gradient(180deg, var(--surface-2) 0%, var(--surface-3) 100%);
}

.message {
  display: flex;
  margin-bottom: 12px;
}

.message.mine {
  justify-content: flex-end;
}

.message-wrapper {
  max-width: 70%;
}

.message-content {
  max-width: 70%;
  padding: 10px 12px;
  border-radius: 14px;
  background: var(--surface-3);
  word-break: break-word;
}

.message.mine .message-content {
  background: var(--primary);
  color: #fff;
}

.message.group-message .message-wrapper {
  max-width: 78%;
}

.message.group-message .message-author {
  font-size: 0.78rem;
  color: var(--muted);
  margin: 0 0 4px 8px;
}

.message-file {
  margin-top: 6px;
  display: inline-block;
  color: inherit;
  text-decoration: underline;
}

.message-time {
  font-size: 0.78rem;
  color: var(--muted);
  margin-top: 4px;
}

.chat-input-area {
  display: flex;
  gap: 10px;
  padding: 14px;
  border-top: 1px solid var(--border);
}

.chat-input-area input[type="text"] {
  flex: 1;
  padding: 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  outline: none;
  background: var(--surface);
}

.chat-input-area button {
  width: 50px;
  background: var(--primary);
  border: none;
  color: #fff;
  border-radius: 10px;
}

.search-result {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--surface);
  border: 1px solid var(--border);
  padding: 12px;
  border-radius: 12px;
}

.search-result button {
  background: var(--success);
  color: #fff;
  border: none;
  padding: 8px 10px;
  border-radius: 8px;
}

.empty-state {
  padding: 20px;
  color: var(--muted);
  text-align: center;
}

.group-modal {
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.5);
  display: grid;
  place-items: center;
  z-index: 1000;
}

.group-modal-card {
  width: min(460px, 90vw);
  background: var(--surface);
  border-radius: 16px;
  padding: 18px;
  border: 1px solid var(--border);
  box-shadow: 0 18px 50px var(--shadow);
}

.group-modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.close-btn {
  background: transparent;
  border: none;
  font-size: 1.4rem;
  color: var(--muted);
}

.group-modal-body input {
  width: 100%;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface);
  margin-bottom: 10px;
}

.save-group-btn,
.group-invite-row button {
  width: 100%;
  padding: 10px;
  border: none;
  background: var(--primary);
  color: #fff;
  border-radius: 10px;
}

.group-member-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 10px 0;
}

.group-member-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--surface-3);
  padding: 5px 8px;
  border-radius: 999px;
  font-size: 0.9rem;
}

.group-member-pill button {
  background: transparent;
  border: none;
  color: var(--muted);
  font-size: 0.9rem;
}

.group-invite-row {
  display: flex;
  gap: 8px;
}

.group-invite-row input {
  flex: 1;
  margin-bottom: 0;
}

.group-invite-row button {
  width: auto;
  white-space: nowrap;
}

.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: rgba(17, 24, 39, 0.88);
  color: #fff;
  padding: 10px 14px;
  border-radius: 999px;
  opacity: 0;
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.message-attachment {
  display: inline-block;
  margin-top: 6px;
  color: inherit;
  text-decoration: underline;
}

.toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

@media (max-width: 900px) {
  .chat-container {
    grid-template-columns: 1fr;
    height: auto;
    min-height: 90vh;
  }

  .sidebar {
    max-height: 50vh;
  }
}