* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}

body {
  background: #f4f6f9;
  padding: 15px;
}

nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: #0d6efd;
  color: white;
  padding: 15px;
  border-radius: 10px;
}

.back-btn {
  color: white;
  text-decoration: none;
}

.invoice-page {
  max-width: 1200px;
  margin: auto;
}

h1 {
  margin: 20px 0;
  text-align: center;
}

.form-section {
  background: white;
  padding: 20px;
  border-radius: 10px;
  margin-bottom: 20px;
}

.form-section h2 {
  margin-bottom: 15px;
}

label {
  display: block;
  margin-top: 10px;
}

input,
textarea {
  width: 100%;
  padding: 10px;
  margin-top: 5px;
  border: 1px solid #ccc;
  border-radius: 6px;
}

button {
  background: #0d6efd;
  color: white;
  border: none;
  padding: 10px 15px;
  border-radius: 6px;
  cursor: pointer;
}

button:hover {
  opacity: .9;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 15px;
}

table th,
table td {
  border: 1px solid #ddd;
  padding: 10px;
  text-align: center;
}

.invoice-summary {
  margin-top: 20px;
  text-align: right;
}

.invoice-preview {
  background: white;
  margin-top: 30px;
  padding: 25px;
  border-radius: 10px;
  display: none;
}

.invoice-header {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  align-items: center;
}

.invoice-header img {
  max-width: 100px;
}

.invoice-actions {
  margin: 20px 0;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.signature {
  display: flex;
  justify-content: space-between;
  margin-top: 50px;
}

@media(max-width:768px) {
  
  .invoice-header {
    flex-direction: column;
    text-align: center;
  }
  
  table {
    display: block;
    overflow-x: auto;
  }
  
  .signature {
    flex-direction: column;
    gap: 30px;
  }
  
  .invoice-actions {
    flex-direction: column;
  }
}