body {
  font-family: Arial, sans-serif;
  background: linear-gradient(135deg, #f5f7fa, #c3cfe2);
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
}

/* MAIN BOX */
.container {
  background: #ffffff;
  padding: 25px;
  width: 100%;
  max-width: 380px;
  border-radius: 15px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.1);
  text-align: center;
}

/* TITLE */
h1 {
  font-size: 22px;
  margin-bottom: 5px;
  color: #222;
}

/* SUBTEXT */
.subtext {
  font-size: 13px;
  color: #666;
  margin-bottom: 20px;
}

/* INPUT + SELECT */
input, select {
  width: 100%;
  padding: 12px;
  margin: 8px 0;
  border: 1px solid #ddd;
  border-radius: 10px;
  font-size: 14px;
  outline: none;
}

input:focus, select:focus {
  border-color: #4a90e2;
}

/* BUTTON GROUP */
.btn-group {
  display: flex;
  gap: 10px;
  margin-top: 10px;
}

/* BUTTONS */
button {
  flex: 1;
  padding: 12px;
  border: none;
  border-radius: 10px;
  font-size: 14px;
  font-weight: bold;
  cursor: pointer;
  transition: 0.2s;
}

/* ADD GST BUTTON */
button:nth-child(1) {
  background: #28a745;
  color: white;
}

button:nth-child(1):hover {
  background: #218838;
}

/* REMOVE GST BUTTON */
button:nth-child(2) {
  background: #dc3545;
  color: white;
}

button:nth-child(2):hover {
  background: #c82333;
}

/* RESULT BOX */
.result {
  margin-top: 20px;
  text-align: left;
  background: #f8f9fa;
  padding: 15px;
  border-radius: 10px;
}

.result p {
  margin: 8px 0;
  font-size: 14px;
  color: #333;
}

/* TOTAL HIGHLIGHT */
.total {
  font-size: 18px;
  font-weight: bold;
  color: #000;
  margin-top: 10px;
}