:root {
  --bg: #f5f5f5;
  --container-bg: #ffffff;
  --text: #1a1a1a;
  --bubble-bot: #e9e9eb;
  --bubble-user: #007aff;
  --bubble-user-text: #ffffff;
  --input-bg: #ffffff;
  --input-border: #d1d1d6;
  --header-bg: #f9f9f9;
  --shadow: 0 2px 12px rgba(0,0,0,0.08);
}
[data-theme="dark"] {
  --bg: #1c1c1e;
  --container-bg: #2c2c2e;
  --text: #e5e5ea;
  --bubble-bot: #3a3a3c;
  --bubble-user: #0a84ff;
  --bubble-user-text: #ffffff;
  --input-bg: #3a3a3c;
  --input-border: #48484a;
  --header-bg: #2c2c2e;
}
[data-theme="ocean"] {
  --bg: #e0f7fa;
  --container-bg: #ffffff;
  --text: #004d40;
  --bubble-bot: #b2dfdb;
  --bubble-user: #00796b;
  --bubble-user-text: #ffffff;
  --input-bg: #ffffff;
  --input-border: #80cbc4;
  --header-bg: #b2dfdb;
}
[data-theme="sunset"] {
  --bg: #fff3e0;
  --container-bg: #ffffff;
  --text: #3e2723;
  --bubble-bot: #ffe0b2;
  --bubble-user: #e65100;
  --bubble-user-text: #ffffff;
  --input-bg: #ffffff;
  --input-border: #ffcc80;
  --header-bg: #ffe0b2;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

.container {
  width: 100%;
  max-width: 700px;
  height: 90vh;
  background: var(--container-bg);
  border-radius: 24px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  transition: background 0.3s;
}

header {
  background: var(--header-bg);
  padding: 16px 24px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--input-border);
}
header h1 { font-size: 1.4rem; font-weight: 600; }
.beta { font-size: 0.8rem; color: #888; margin-left: 4px; }
.controls select {
  padding: 6px 12px;
  border-radius: 8px;
  border: 1px solid var(--input-border);
  background: var(--input-bg);
  color: var(--text);
  font-size: 0.9rem;
}

main#chat-window {
  flex: 1;
  overflow-y: auto;
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.message {
  display: flex;
  gap: 12px;
  max-width: 85%;
  animation: fadeIn 0.3s ease;
}
.message.user { align-self: flex-end; flex-direction: row-reverse; }
.message.bot { align-self: flex-start; }

.avatar {
  width: 36px; height: 36px;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  background: var(--bubble-bot);
  font-size: 1.2rem;
  flex-shrink: 0;
}
.message.user .avatar { background: var(--bubble-user); }

.bubble {
  background: var(--bubble-bot);
  padding: 12px 16px;
  border-radius: 18px;
  border-bottom-left-radius: 4px;
  font-size: 0.95rem;
  line-height: 1.5;
  white-space: pre-wrap;
  word-break: break-word;
}
.message.user .bubble {
  background: var(--bubble-user);
  color: var(--bubble-user-text);
  border-bottom-left-radius: 18px;
  border-bottom-right-radius: 4px;
}

footer {
  border-top: 1px solid var(--input-border);
  padding: 12px 20px;
  background: var(--header-bg);
  transition: background 0.3s;
}

form { display: flex; gap: 8px; }
form input {
  flex: 1;
  padding: 12px 16px;
  border: 1px solid var(--input-border);
  border-radius: 24px;
  background: var(--input-bg);
  color: var(--text);
  font-size: 1rem;
  outline: none;
  transition: border 0.2s;
}
form input:focus { border-color: #007aff; }
form button {
  padding: 12px 18px;
  border: none; background: #007aff; color: white;
  border-radius: 50%; font-size: 1.2rem;
  cursor: pointer; transition: opacity 0.2s;
}
form button:disabled { opacity: 0.5; cursor: not-allowed; }

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