:root {
  color-scheme: light;
  --bg: #f4f6f8;
  --panel: #ffffff;
  --panel-soft: #f8fafc;
  --text: #172033;
  --muted: #637083;
  --border: #d8dee8;
  --primary: #1769aa;
  --primary-dark: #0f4f82;
  --danger: #b42318;
  --shadow: 0 12px 30px rgba(22, 32, 51, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  font-family:
    Inter, "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
}

button,
textarea,
input {
  font: inherit;
}

button {
  border: 0;
  border-radius: 6px;
  cursor: pointer;
}

.app-shell {
  display: grid;
  grid-template-columns: 340px minmax(0, 1fr);
  gap: 20px;
  min-height: 100vh;
  padding: 20px;
}

.sidebar,
.chat-panel,
.documents-view {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.sidebar {
  display: flex;
  flex-direction: column;
  min-width: 0;
}

.brand,
.chat-header,
.panel-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.brand {
  padding: 20px;
  border-bottom: 1px solid var(--border);
}

.main-nav {
  display: grid;
  gap: 8px;
  padding: 16px;
}

.nav-item {
  width: 100%;
  padding: 12px 14px;
  background: transparent;
  color: var(--text);
  text-align: left;
}

.nav-item:hover,
.nav-item.active {
  background: #e7f0fa;
  color: var(--primary-dark);
}

h1,
h2,
p {
  margin: 0;
}

h1 {
  font-size: 24px;
  line-height: 1.2;
}

h2 {
  font-size: 17px;
}

.brand p,
.chat-header p,
.status,
.document-meta,
.document-detail,
.source-title {
  color: var(--muted);
  font-size: 13px;
}

.session-badge {
  max-width: 110px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 5px 9px;
  color: var(--muted);
  font-size: 12px;
}

.upload-panel,
.documents-panel,
.section-header {
  padding: 18px 20px;
  border-bottom: 1px solid var(--border);
}

.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.section-header p {
  margin-top: 4px;
  color: var(--muted);
  font-size: 13px;
}

.section-header button {
  background: var(--panel-soft);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 8px 12px;
}

.file-picker {
  display: block;
  border: 1px dashed var(--border);
  border-radius: 8px;
  padding: 16px;
  background: var(--panel-soft);
  color: var(--muted);
  cursor: pointer;
  text-align: center;
}

.file-picker input {
  display: none;
}

.upload-panel button,
.composer button {
  width: 100%;
  margin-top: 12px;
  padding: 11px 14px;
  background: var(--primary);
  color: white;
}

.upload-panel button:hover,
.composer button:hover {
  background: var(--primary-dark);
}

.upload-panel button:disabled,
.composer button:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.status {
  min-height: 18px;
  margin-top: 10px;
}

.panel-heading {
  margin-bottom: 12px;
}

.panel-heading button {
  background: var(--panel-soft);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 7px 10px;
}

.document-list {
  display: grid;
  gap: 8px;
}

.document-item {
  display: block;
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px;
  background: white;
  text-align: left;
}

.document-title {
  display: block;
  overflow-wrap: anywhere;
  font-weight: 650;
}

.document-detail {
  display: block;
  margin-top: 4px;
}

.document-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-top: 8px;
}

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

.download-document {
  background: transparent;
  color: var(--primary);
  padding: 4px 0;
}

.delete-document {
  background: transparent;
  color: var(--danger);
  padding: 4px 0;
}

.empty {
  color: var(--muted);
  font-size: 14px;
  padding: 18px 0;
}

.chat-panel {
  display: grid;
  grid-template-rows: auto minmax(0, 1fr) auto;
  min-width: 0;
}

.documents-view {
  display: flex;
  flex-direction: column;
  min-width: 0;
}

.app-view {
  display: none;
}

.app-view.active {
  display: grid;
}

.documents-view.app-view.active {
  display: flex;
}

.chat-header {
  padding: 20px;
  border-bottom: 1px solid var(--border);
}

.chat-status {
  min-height: 18px;
  padding: 10px 20px 0;
  color: var(--muted);
  font-size: 13px;
}

.source-toggle {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  white-space: nowrap;
}

.messages {
  overflow-y: auto;
  padding: 20px;
}

.message {
  max-width: 820px;
  margin-bottom: 16px;
  padding: 13px 15px;
  border-radius: 8px;
  line-height: 1.55;
  white-space: pre-wrap;
}

.message.user {
  margin-left: auto;
  background: #e7f0fa;
}

.message.assistant {
  background: var(--panel-soft);
  border: 1px solid var(--border);
}

.message.pending {
  color: var(--muted);
}

.sources {
  display: grid;
  gap: 8px;
  margin-top: 10px;
}

.source {
  border-left: 3px solid var(--primary);
  padding: 8px 10px;
  background: white;
  color: var(--muted);
  font-size: 13px;
}

.source-title {
  display: block;
  margin-bottom: 4px;
  color: var(--text);
  font-weight: 650;
}

.composer {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 120px;
  gap: 12px;
  padding: 18px 20px;
  border-top: 1px solid var(--border);
}

.composer textarea {
  width: 100%;
  resize: vertical;
  min-height: 48px;
  max-height: 150px;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 11px 12px;
  color: var(--text);
}

.composer button {
  margin: 0;
}

@media (max-width: 860px) {
  .app-shell {
    grid-template-columns: 1fr;
    padding: 12px;
  }

  .chat-panel {
    min-height: 620px;
  }

  .composer {
    grid-template-columns: 1fr;
  }
}