:root {
    --bg-color: #f3f4f6; /* Soft light gray background */
    --card-bg: #ffffff; /* Pure white card */
    --text-primary: #111827; /* Near black text */
    --text-secondary: #4b5563; /* Gray text */
    --primary-color: #0f766e; /* Deep teal/green */
    --primary-hover: #115e59;
    --border-color: #e5e7eb;
    --focus-ring: rgba(15, 118, 110, 0.2);
    --error-color: #ef4444;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
}

.container {
    max-width: 800px;
    width: 100%;
    margin: 40px 20px;
    background-color: var(--card-bg);
    border-radius: 20px;
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.05);
    padding: 50px;
    box-sizing: border-box;
}

h1 {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--primary-color);
    margin-top: 0;
    margin-bottom: 30px;
    letter-spacing: -0.02em;
}

h2 {
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-top: 40px;
    margin-bottom: 20px;
    padding-bottom: 12px;
    border-bottom: 2px solid var(--border-color);
}

.calculator {
    background-color: #f8fafc;
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 35px;
    margin-bottom: 40px;
    box-shadow: 0 4px 6px -1px rgba(0,0,0,0.02);
}

.input-group {
    margin-bottom: 24px;
}

.input-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.input-group input {
    width: 100%;
    padding: 14px 18px;
    background-color: #ffffff;
    border: 1px solid #d1d5db;
    border-radius: 10px;
    color: var(--text-primary);
    font-size: 1rem;
    box-sizing: border-box;
    transition: all 0.2s ease;
    font-family: inherit;
}

.input-group input::placeholder {
    color: #9ca3af;
}

.input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px var(--focus-ring);
}

button {
    width: 100%;
    padding: 16px;
    background-color: var(--primary-color);
    color: #ffffff;
    border: none;
    border-radius: 10px;
    font-size: 1.125rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    margin-top: 10px;
    letter-spacing: 0.01em;
}

button:hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: 0 4px 6px -1px rgba(0,0,0,0.1);
}

button:active {
    transform: translateY(0);
}

#result {
    margin-top: 25px;
    padding: 20px;
    border-radius: 10px;
    text-align: center;
    font-size: 1.5rem;
    font-weight: 700;
    display: none;
}

.success {
    background-color: #ecfdf5;
    color: #065f46;
    border: 1px solid #a7f3d0;
}

.error {
    background-color: #fef2f2;
    color: #991b1b;
    border: 1px solid #fecaca;
    font-size: 1rem !important;
}

.error-msg {
    color: var(--error-color);
    font-size: 0.875rem;
    margin-top: 6px;
    display: none;
    font-weight: 500;
}

.content-section {
    color: var(--text-secondary);
}

.content-section p {
    margin-bottom: 20px;
    font-size: 1.05rem;
    line-height: 1.7;
}

.content-section strong {
    color: var(--text-primary);
}

.content-section ul {
    margin-bottom: 20px;
    padding-left: 20px;
}

.content-section li {
    margin-bottom: 10px;
    font-size: 1.05rem;
    line-height: 1.7;
}

.faq-item {
    margin-bottom: 20px;
    background-color: #f9fafb;
    padding: 20px 24px;
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

.faq-question {
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--text-primary);
    font-size: 1.1rem;
}

.faq-answer {
    color: var(--text-secondary);
    margin-bottom: 0;
    font-size: 1.05rem;
    line-height: 1.6;
}

.formula-box {
    background-color: #f0fdfa;
    padding: 24px;
    border-radius: 12px;
    border: 1px solid #ccfbf1;
    text-align: center;
    font-size: 1.25rem;
    font-weight: 700;
    color: #0f766e;
    margin: 30px 0;
}

@media (max-width: 600px) {
    .container {
        padding: 30px 20px;
        margin: 20px 10px;
        border-radius: 16px;
    }
    h1 {
        font-size: 2rem;
    }
    .calculator {
        padding: 20px;
    }
}