* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  font-family: Arial, sans-serif;
  background: #f5f7fa;
  color: #333;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}
.container {
  background: #fff;
  max-width: 800px;
  width: 90%;
  margin: 20px;
  padding: 20px;
  border-radius: 10px;
  box-shadow: 0 4px 15px rgba(0,0,0,0.1);
  display: flex;
  flex-direction: column;
  height: 80vh;
}
header {
  text-align: center;
  margin-bottom: 10px;
}
header h1 {
  background: linear-gradient(90deg, #667eea, #764ba2);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}
.chat-window {
  flex: 1;
  overflow-y: auto;
  padding: 10px;
  border: 1px solid #e1e4e8;
  border-radius: 8px;
  background: #fafbfc;
  margin-bottom: 10px;
  display: flex;
  flex-direction: column;
}
.message {
  margin: 5px 0;
  padding: 8px 12px;
  border-radius: 8px;
  max-width: 70%;
  word-wrap: break-word;
  box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}
.message.sent {
  background: #daf8cb;
  align-self: flex-end;
}
.message.received {
  background: #e2e8f0;
  align-self: flex-start;
}
.chat-form {
  display: flex;
}
.chat-form input {
  flex: 1;
  padding: 10px;
  border: 1px solid #ccd0d5;
  border-radius: 8px 0 0 8px;
  outline: none;
}
.chat-form button {
  padding: 10px 20px;
  border: none;
  background: #667eea;
  color: #fff;
  border-radius: 0 8px 8px 0;
  cursor: pointer;
  transition: background 0.3s ease;
}
.chat-form button:hover {
  background: #556cd6;
}
footer {
  text-align: center;
  margin-top: 10px;
  font-size: 0.9em;
  color: #777;
}
@media (max-width: 600px) {
  .container {
    height: 90vh;
  }
}