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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.8;
    color: #333;
    background-color: #f5f7fa;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background-color: #fff;
    padding: 20px 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-size: 32px;
    font-weight: bold;
    color: #D32F2F;
    text-decoration: none;
    letter-spacing: 2px;
    text-transform: uppercase;
}

nav ul {
    list-style: none;
    display: flex;
    gap: 30px;
}

nav ul li a {
    color: #37474F;
    text-decoration: none;
    font-size: 16px;
    font-weight: 500;
    transition: color 0.3s;
}

nav ul li a:hover {
    color: #D32F2F;
}

.hero {
    background: linear-gradient(rgba(55, 71, 79, 0.85), rgba(55, 71, 79, 0.7)), url('imgs/hero-blood-cells.jpg');
    background-size: cover;
    background-position: center;
    height: 550px;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    color: #fff;
}

.hero-content h1 {
    font-size: 52px;
    margin-bottom: 20px;
    font-weight: bold;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.5);
    letter-spacing: 1px;
}

.hero-content p {
    font-size: 22px;
    max-width: 750px;
    margin: 0 auto;
    line-height: 1.6;
    opacity: 0.95;
}

.content-section {
    padding: 70px 0;
    background-color: #fff;
    border-bottom: 1px solid #e0e0e0;
}

.content-section:nth-child(even) {
    background-color: #f5f7fa;
}

.content-section:last-of-type {
    border-bottom: none;
}

.content-section h2 {
    font-size: 34px;
    color: #37474F;
    margin-bottom: 30px;
    position: relative;
    padding-bottom: 20px;
}

.content-section h2::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 80px;
    height: 4px;
    background-color: #D32F2F;
}

.content-section p {
    font-size: 18px;
    margin-bottom: 25px;
    text-align: justify;
    color: #555;
    line-height: 1.9;
}

.section-image {
    width: 100%;
    max-width: 850px;
    height: 420px;
    object-fit: cover;
    border-radius: 10px;
    margin: 35px 0;
    box-shadow: 0 8px 30px rgba(0,0,0,0.12);
}

.content-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 50px;
    align-items: center;
}

.content-grid.reverse {
    direction: rtl;
}

.content-grid.reverse > * {
    direction: ltr;
}

.text-content h3 {
    font-size: 26px;
    color: #37474F;
    margin-bottom: 20px;
    font-weight: 600;
}

.text-content p {
    font-size: 17px;
    line-height: 1.95;
}

.image-content img {
    width: 100%;
    height: 380px;
    object-fit: cover;
    border-radius: 10px;
    box-shadow: 0 6px 25px rgba(0,0,0,0.1);
}

footer {
    background-color: #37474F;
    color: #fff;
    padding: 60px 0 30px;
    margin-top: 60px;
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 35px;
    margin-bottom: 45px;
}

.footer-section h4 {
    font-size: 20px;
    margin-bottom: 22px;
    color: #D32F2F;
    font-weight: 600;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: 14px;
}

.footer-section ul li a {
    color: #fff;
    text-decoration: none;
    font-size: 15px;
    transition: color 0.3s;
    opacity: 0.9;
}

.footer-section ul li a:hover {
    color: #D32F2F;
}

.footer-section p {
    font-size: 15px;
    line-height: 1.85;
    color: #fff;
    opacity: 0.9;
}

.footer-bottom {
    text-align: center;
    padding-top: 35px;
    border-top: 1px solid rgba(255,255,255,0.15);
    font-size: 14px;
    opacity: 0.85;
}

.page-header {
    background: linear-gradient(rgba(55, 71, 79, 0.9), rgba(55, 71, 79, 0.7)), url('imgs/heart-visualization.jpg');
    background-size: cover;
    background-position: center;
    height: 280px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #fff;
}

.page-header h1 {
    font-size: 46px;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.5);
    letter-spacing: 1px;
}

.page-content {
    padding: 70px 0;
    max-width: 950px;
    margin: 0 auto;
}

.page-content h2 {
    font-size: 30px;
    color: #37474F;
    margin: 45px 0 25px;
    border-bottom: 3px solid #D32F2F;
    padding-bottom: 12px;
}

.page-content h3 {
    font-size: 24px;
    color: #37474F;
    margin: 35px 0 18px;
    font-weight: 600;
}

.page-content p {
    font-size: 18px;
    line-height: 1.95;
    margin-bottom: 22px;
    text-align: justify;
}

.page-content ul {
    margin: 22px 0 22px 45px;
}

.page-content ul li {
    font-size: 18px;
    line-height: 1.9;
    margin-bottom: 12px;
}

@media (max-width: 768px) {
    header .container {
        flex-direction: column;
        gap: 18px;
    }

    nav ul {
        flex-wrap: wrap;
        justify-content: center;
        gap: 18px;
    }

    .hero {
        height: 450px;
    }

    .hero-content h1 {
        font-size: 36px;
    }

    .hero-content p {
        font-size: 19px;
    }

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

    .content-grid.reverse {
        direction: ltr;
    }

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

    .section-image {
        height: 280px;
    }

    .image-content img {
        height: 300px;
    }
}

@media (max-width: 480px) {
    .footer-content {
        grid-template-columns: 1fr;
    }

    .hero-content h1 {
        font-size: 28px;
    }

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