.center {
  margin: auto;
  width: 75%;
  border: 3px solid #73AD21;
  padding: 100px;
}

div {
  background-color: lightblue;
  width: 500px;
  height: 400px;
  border: 20px solid green;
  padding: 100px;
  margin: 20px;
}
body {
    background-color: #f4f7f6; /* Soft, light background */
    font-family: Arial, sans-serif;
    display: flex; /* Helps with centering */
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

/* 2. LAYER 2: The Calculator Card (Structure & Box Look) */
.calculator-card {
    background-color: white; /* Clean foreground box */
    padding: 30px;
    border-radius: 10px; /* Rounded corners */
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1); /* Subtle shadow for depth */
    width: 100%;
    max-width: 350px; /* Keeps the box short and narrow */
    text-align: center; /* Centers the title and button */
}

/* 3. Input Group Styling (Stacking and Sizing) */
.input-group {
    text-align: left; /* Aligns the label to the left */
    margin-bottom: 15px;
}

label {
    display: block; /* Makes the label take its own line */
    margin-bottom: 5px;
    font-weight: bold;
    color: #555;
}

input[type="number"] {
    width: 100%; /* Makes input take full width of the 350px card */
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: 5px;
    box-sizing: border-box; 
    font-size: 16px;
}

/* 4. Button and Result Styling */
button {
    width: 100%;
    padding: 12px;
    margin-top: 10px;
    background-color: #007bff; /* Primary action color */
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 16px;
    cursor: pointer;
    transition: background-color 0.3s;
}

.result-display {
    margin-top: 25px;
    padding: 15px;
    background-color: #e9ecef; /* Background for the result box */
    border-radius: 5px;
    font-size: 1.1em;
    font-weight: bold;
    color: #333;
}