body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
    display: flex;
    justify-content: center;
    align-items: flex-start; /* Align to top to better see content if it grows */
    min-height: 100vh;
    background-color: #f0f4f8; /* Lighter, more modern blue-grey */
    margin: 0;
    padding: 20px;
    box-sizing: border-box;
    color: #333;
}

.container {
    background-color: #ffffff;
    padding: 25px 30px;
    border-radius: 12px;
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 550px; /* Slightly wider for comfort */
    margin-top: 20px; /* Ensure some space from top on small screens */
}

h1 {
    color: #2c3e50; /* Darker, more professional blue */
    text-align: center;
    margin-bottom: 30px;
    font-size: 1.8em;
}

.input-group {
    margin-bottom: 22px;
}

.input-group label {
    display: block;
    margin-bottom: 8px;
    color: #34495e; /* Slightly desaturated blue */
    font-weight: 600; /* Bolder labels */
    font-size: 0.95em;
}

.input-group input[type="number"] {
    width: 100%; /* Simpler width calculation */
    padding: 12px;
    border: 1px solid #bdc3c7; /* Softer grey border */
    border-radius: 6px;
    font-size: 1em;
    box-sizing: border-box; /* Include padding and border in element's total width and height */
    transition: border-color 0.3s ease, box-shadow 0.3s ease;
}

.input-group input[type="number"]:focus {
    border-color: #3498db; /* Blue focus highlight */
    box-shadow: 0 0 0 2px rgba(52, 152, 219, 0.2);
    outline: none;
}


button {
    display: block;
    width: 100%;
    padding: 14px;
    background: linear-gradient(145deg, #3498db, #2980b9); /* Gradient blue */
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1.15em;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s ease, transform 0.1s ease;
    margin-top: 25px;
    box-shadow: 0 4px 6px rgba(50, 50, 93, 0.11), 0 1px 3px rgba(0, 0, 0, 0.08);
}

button:hover {
    background: linear-gradient(145deg, #2980b9, #1f6a9c); /* Darker gradient */
}

button:active {
    transform: translateY(1px);
}

.results-container {
    margin-top: 35px;
    padding-top: 25px;
    border-top: 1px solid #e0e0e0; /* Lighter separator */
}

.results-container h2 {
    color: #2c3e50;
    margin-bottom: 20px;
    font-size: 1.5em;
}

.results-container p {
    font-size: 1.1em;
    color: #34495e;
    margin-bottom: 12px;
    line-height: 1.7;
    background-color: #f8f9fa;
    padding: 10px;
    border-radius: 4px;
    border-left: 4px solid #3498db;
}

.results-container p#paybackPeriod {
    border-left-color: #2ecc71; /* Green for payback */
}

/* Basic error styling for inputs (can be added via JS if needed) */
.input-group input.error {
    border-color: #e74c3c; /* Red for error */
    box-shadow: 0 0 0 2px rgba(231, 76, 60, 0.2);
}

/* Hide number input spinners for a cleaner look (optional) */
input[type=number]::-webkit-inner-spin-button,
input[type=number]::-webkit-outer-spin-button {
  -webkit-appearance: none;
  margin: 0;
}
input[type=number] {
  -moz-appearance: textfield; /* Firefox */
}