* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background: #f5f7fb;
    color: #1f2937;
    line-height: 1.6;
}

.hero {
    min-height: 100vh;
    background:
            linear-gradient(rgba(15, 23, 42, 0.75), rgba(15, 23, 42, 0.75)),
            radial-gradient(circle at top left, #38bdf8, transparent 35%),
            linear-gradient(135deg, #0f172a, #1e3a8a);
    color: white;
}

.navbar {
    max-width: 1150px;
    margin: 0 auto;
    padding: 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 1.4rem;
    font-weight: 800;
}

.nav-links {
    display: flex;
    gap: 22px;
}

.nav-links a {
    color: #e0f2fe;
    text-decoration: none;
    font-weight: 600;
    transition: color 0.2s ease;
}

.nav-links a:hover {
    color: #38bdf8;
}

.hero-content {
    max-width: 850px;
    margin: 0 auto;
    padding: 160px 24px 80px;
    text-align: center;
}

.hero-content h1 {
    font-size: clamp(2.5rem, 7vw, 5.5rem);
    line-height: 1.05;
    margin-bottom: 24px;
}

.hero-content p {
    font-size: 1.25rem;
    color: #dbeafe;
    max-width: 680px;
    margin: 0 auto 36px;
}

.hero-button {
    display: inline-block;
    padding: 15px 28px;
    background: #38bdf8;
    color: #082f49;
    border-radius: 999px;
    text-decoration: none;
    font-weight: 800;
    box-shadow: 0 18px 40px rgba(56, 189, 248, 0.35);
    transition: transform 0.2s ease, background 0.2s ease;
}

.hero-button:hover {
    background: #7dd3fc;
    transform: translateY(-3px);
}

.section {
    max-width: 1150px;
    margin: 0 auto;
    padding: 85px 24px;
}

.section h2 {
    font-size: clamp(2rem, 4vw, 3rem);
    margin-bottom: 18px;
    color: #0f172a;
}

.section > p {
    max-width: 760px;
    color: #475569;
    margin-bottom: 28px;
}

.formula-card {
    margin-top: 32px;
    padding: 28px;
    background: white;
    border-radius: 24px;
    box-shadow: 0 20px 45px rgba(15, 23, 42, 0.08);
    border: 1px solid #e2e8f0;
}

.formula-card span {
    display: block;
    color: #64748b;
    margin-bottom: 8px;
}

.formula-card strong {
    font-size: 2rem;
    color: #2563eb;
}

.calculator-section {
    background: linear-gradient(135deg, #eff6ff, #f8fafc);
    max-width: none;
}

.calculator-section h2,
.calculator-section > p,
.calculator-card {
    max-width: 850px;
    margin-left: auto;
    margin-right: auto;
}

.calculator-card {
    background: white;
    padding: 34px;
    border-radius: 26px;
    box-shadow: 0 25px 50px rgba(37, 99, 235, 0.12);
    border: 1px solid #dbeafe;
}

.calculator-card label {
    display: block;
    font-weight: 800;
    margin-bottom: 10px;
}

select,
button {
    width: 100%;
    padding: 15px 16px;
    border-radius: 14px;
    font-size: 1rem;
}

select {
    border: 1px solid #cbd5e1;
    margin-bottom: 18px;
    background: #f8fafc;
}

button {
    border: none;
    background: #2563eb;
    color: white;
    font-weight: 800;
    cursor: pointer;
    transition: background 0.2s ease, transform 0.2s ease;
}

button:hover {
    background: #1d4ed8;
    transform: translateY(-2px);
}

.result-box {
    margin-top: 24px;
    padding: 24px;
    background: #f8fafc;
    border-radius: 18px;
    border: 1px dashed #93c5fd;
}

.result-box p {
    color: #64748b;
    margin-bottom: 8px;
}

.result-box h3 {
    color: #1e40af;
    font-size: 1.5rem;
}

.grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
    margin-top: 34px;
}

.info-card {
    background: white;
    padding: 28px;
    border-radius: 24px;
    box-shadow: 0 18px 40px rgba(15, 23, 42, 0.07);
    border: 1px solid #e2e8f0;
}

.info-card h3 {
    color: #1d4ed8;
    margin-bottom: 12px;
}

.info-card p {
    color: #475569;
    margin-bottom: 16px;
}

code {
    display: inline-block;
    background: #eef6ff;
    color: #075985;
    padding: 8px 12px;
    border-radius: 10px;
    font-weight: 700;
}

.facts-section {
    padding-top: 40px;
}

.facts-list {
    display: grid;
    gap: 18px;
    margin-top: 32px;
}

.fact {
    display: flex;
    gap: 22px;
    align-items: flex-start;
    background: white;
    padding: 24px;
    border-radius: 22px;
    border: 1px solid #e2e8f0;
    box-shadow: 0 12px 35px rgba(15, 23, 42, 0.06);
}

.fact span {
    min-width: 54px;
    height: 54px;
    background: #dbeafe;
    color: #1d4ed8;
    display: grid;
    place-items: center;
    border-radius: 16px;
    font-weight: 900;
}

.fact p {
    color: #475569;
}

footer {
    text-align: center;
    padding: 28px;
    background: #0f172a;
    color: #cbd5e1;
}

@media (max-width: 760px) {
    .navbar {
        flex-direction: column;
        gap: 18px;
    }

    .nav-links {
        flex-wrap: wrap;
        justify-content: center;
    }

    .hero-content {
        padding-top: 100px;
    }

    .grid {
        grid-template-columns: 1fr;
    }

    .formula-card strong {
        font-size: 1.5rem;
    }
}