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

html {
    scroll-behavior: smooth;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background: #f8fafc;
    color: #1e293b;
    line-height: 1.6;
}

.container {
    width: min(1100px, 92%);
    margin: 0 auto;
}


/* Header */

.site-header {
    background: #ffffff;
    border-bottom: 1px solid #e2e8f0;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.header-inner {
    min-height: 70px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
}

.logo {
    color: #0f172a;
    text-decoration: none;
    font-size: 20px;
    font-weight: 700;
}

nav {
    display: flex;
    gap: 25px;
}

nav a {
    color: #475569;
    text-decoration: none;
    font-size: 15px;
    font-weight: 600;
}

nav a:hover {
    color: #2563eb;
}


/* Hero */

.hero {
    text-align: center;
    padding: 80px 0 70px;
    background: linear-gradient(135deg, #eff6ff, #ffffff);
}

.badge {
    display: inline-block;
    padding: 6px 14px;
    margin-bottom: 18px;
    border-radius: 30px;
    background: #dbeafe;
    color: #1d4ed8;
    font-size: 14px;
    font-weight: 700;
}

.hero h1 {
    font-size: clamp(36px, 6vw, 58px);
    line-height: 1.1;
    margin-bottom: 20px;
    color: #0f172a;
}

.hero p {
    max-width: 700px;
    margin: 0 auto 30px;
    color: #475569;
    font-size: 18px;
}

.hero-button {
    display: inline-block;
    padding: 13px 22px;
    background: #2563eb;
    color: #ffffff;
    text-decoration: none;
    border-radius: 8px;
    font-weight: 700;
}

.hero-button:hover {
    background: #1d4ed8;
}


/* Calculator */

.calculator-section {
    padding: 70px 0;
}

.calculator-card {
    max-width: 600px;
    margin: 0 auto;
    background: #ffffff;
    padding: 35px;
    border-radius: 16px;
    box-shadow: 0 10px 35px rgba(15, 23, 42, 0.08);
    border: 1px solid #e2e8f0;
}

.calculator-card h2 {
    text-align: center;
    font-size: 28px;
    margin-bottom: 10px;
    color: #0f172a;
}

.calculator-description {
    text-align: center;
    color: #64748b;
    margin-bottom: 30px;
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 700;
    color: #334155;
}

.form-group input {
    width: 100%;
    padding: 14px 15px;
    border: 1px solid #cbd5e1;
    border-radius: 8px;
    font-size: 16px;
    outline: none;
    background: #ffffff;
}

.form-group input:focus {
    border-color: #2563eb;
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.12);
}

.button-row {
    display: flex;
    gap: 12px;
    margin-top: 25px;
}

.calculate-btn,
.reset-btn {
    border: none;
    padding: 14px 20px;
    border-radius: 8px;
    font-size: 16px;
    font-weight: 700;
    cursor: pointer;
}

.calculate-btn {
    flex: 1;
    background: #2563eb;
    color: #ffffff;
}

.calculate-btn:hover {
    background: #1d4ed8;
}

.reset-btn {
    background: #e2e8f0;
    color: #334155;
}

.reset-btn:hover {
    background: #cbd5e1;
}


/* Error */

.error {
    min-height: 24px;
    margin-top: 15px;
    color: #dc2626;
    font-size: 14px;
    font-weight: 600;
}


/* Result */

.result {
    display: none;
    margin-top: 20px;
    padding: 25px;
    border-radius: 12px;
    text-align: center;
    background: #eff6ff;
    border: 1px solid #bfdbfe;
}

.result-label {
    color: #475569;
    font-size: 15px;
    font-weight: 700;
    margin-bottom: 8px;
}

.required-grade {
    color: #1d4ed8;
    font-size: 32px;
    font-weight: 800;
    margin-bottom: 8px;
}

.result-message {
    color: #475569;
    font-size: 14px;
}


/* Content */

.content-section {
    padding: 70px 0;
    background: #ffffff;
}

.content-section:nth-of-type(even) {
    background: #f8fafc;
}

.content-container {
    max-width: 850px;
}

.content-section h2 {
    color: #0f172a;
    font-size: 32px;
    margin-bottom: 20px;
}

.content-section h3 {
    color: #0f172a;
    font-size: 22px;
    margin: 30px 0 12px;
}

.content-section p {
    color: #475569;
    margin-bottom: 18px;
}

.content-section ul {
    margin: 0 0 20px 22px;
    color: #475569;
}

.formula {
    margin: 25px 0;
    padding: 20px;
    background: #f1f5f9;
    border-left: 4px solid #2563eb;
    border-radius: 6px;
    font-weight: 700;
    color: #1e293b;
    overflow-x: auto;
}


/* FAQ */

.faq-item {
    padding: 22px 0;
    border-bottom: 1px solid #e2e8f0;
}

.faq-item h3 {
    margin-top: 0;
    font-size: 20px;
}


/* Footer */

.site-footer {
    background: #0f172a;
    color: #cbd5e1;
    text-align: center;
    padding: 35px 0;
}

.site-footer p {
    margin: 5px 0;
}


/* Mobile */

@media (max-width: 700px) {

    .header-inner {
        flex-direction: column;
        justify-content: center;
        padding: 15px 0;
    }

    nav {
        gap: 15px;
        flex-wrap: wrap;
        justify-content: center;
    }

    .hero {
        padding: 60px 0 50px;
    }

    .hero h1 {
        font-size: 40px;
    }

    .hero p {
        font-size: 16px;
    }

    .calculator-card {
        padding: 25px 20px;
    }

    .calculator-card h2 {
        font-size: 24px;
    }

    .button-row {
        flex-direction: column;
    }

    .calculate-btn,
    .reset-btn {
        width: 100%;
    }

    .content-section {
        padding: 50px 0;
    }

    .content-section h2 {
        font-size: 28px;
    }

    .required-grade {
        font-size: 27px;
    }
}