body {
  margin: 0;
  font-family: 'Segoe UI', sans-serif;
  background: #f7f7fa;
  color: #222;
}
header {
  background: #5b9bd5;
  color: #fff;
  padding: 1em 0.5em;
  text-align: center;
}
h1 {
  margin: 0;
  font-weight: bold;
  font-size: 1.4em;
}
nav {
  margin-top: 0.5em;
}
main {
  max-width: 480px;
  margin: 2em auto;
  background: #fff;
  border-radius: 8px;
  box-shadow: 0 2px 10px #ddd;
  padding: 1em;
}
#authSection {
  text-align: center;
}
#authTabs {
  display: flex;
  justify-content: center;
  margin-bottom: 1em;
}
#authTabs button {
  flex: 1;
  padding: 0.5em;
  border: none;
  background: #eaeaea;
  cursor: pointer;
  font-size: 1em;
}
#authTabs button.active {
  background: #5b9bd5;
  color: #fff;
}
form {
  margin-bottom: 1em;
}
form input, form button {
  width: 90%;
  margin: 0.3em auto;
  display: block;
  padding: 0.5em;
  font-size: 1em;
  border-radius: 5px;
  border: 1px solid #bbb;
  box-sizing: border-box;
}
form button {
  background: #5b9bd5;
  color: #fff;
  border: none;
  margin-top: 0.7em;
}
#expenseTable, #userTable {
  width: 100%;
  border-collapse: collapse;
  margin-top: 1em;
  background: #fefefe;
}
#expenseTable th, #expenseTable td, #userTable th, #userTable td {
  border: 1px solid #eee;
  padding: 0.5em;
  text-align: center;
}
#expenseTable th, #userTable th {
  background: #f0f5fa;
}
.user-info {
  margin-bottom: 1em;
  font-size: 0.95em;
  color: #666;
}
#aiSummaryBtn {
  margin-top: 1em;
  background: #f6b26b;
  border: none;
  color: #fff;
  padding: 0.7em 1.2em;
  border-radius: 5px;
  cursor: pointer;
}
#aiSummaryResult {
  margin: 1em 0;
  white-space: pre-line;
  background: #f9f7e8;
  border-left: 4px solid #f6b26b;
  padding: 0.6em;
  font-size: 0.96em;
}
#expenseMessage, #authMessage {
  color: #d9534f;
  min-height: 1.5em;
  margin-bottom: 0.5em;
}
@media (max-width: 600px) {
  main {
    padding: 0.4em;
    margin: 0.5em;
  }
  table, th, td {
    font-size: 0.97em;
  }
}