body {
  font-family: sans-serif;
  margin: 0;
  padding: 0;
  background: #f4f4f4;
}
.input-bar {
  display: flex;
  padding: 10px;
  background: #fff;
  border-bottom: 1px solid #ddd;
}
.input-bar input, .input-bar button {
  margin-right: 10px;
  padding: 8px;
  font-size: 1rem;
}
#main {
  padding: 20px;
}
#summary, #categories, #expenses {
  list-style: none;
  padding: 0;
}
#summary li, #categories li, #expenses li {
  background: #fff;
  margin-bottom: 10px;
  padding: 10px;
  border: 1px solid #ddd;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
button {
  cursor: pointer;
}
.overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.5);
  display: flex;
  justify-content: center;
  align-items: center;
}
.hidden {
  display: none;
}
.popup {
  background: #fff;
  padding: 20px;
  max-width: 90%;
  width: 300px;
  border-radius: 4px;
}
.popup h2 {
  margin-top: 0;
}
.popup input {
  width: calc(100% - 20px);
  padding: 8px;
  margin-bottom: 10px;
}
.popup button {
  margin-right: 10px;
  padding: 8px 12px;
}
.popup .delete-btn {
  background: transparent;
  border: none;
  color: #f00;
}