body {
    font-family: Arial, sans-serif;
    background-color: #E3F2FD;
    color: #0D47A1;
    margin: 0;
    padding: 0;
}

header {
    background-color: #BBDEFB;
    padding: 20px;
    text-align: center;
}

header h1 {
    margin: 0;
    color: #0D47A1;
}

nav {
    display: flex;
    justify-content: center;
    background-color: #90CAF9;
    padding: 10px;
}

nav a {
    margin: 0 15px;
    text-decoration: none;
    color: #0D47A1;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
}

.card {
    background-color: #E3F2FD;
    border: 1px solid #90CAF9;
    border-radius: 8px;
    padding: 20px;
    margin-bottom: 20px;
}

.card h2 {
    margin-top: 0;
    color: #0D47A1;
}

.card-content {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: flex-start;
}

.card-content img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
}

.challenge-list {
    list-style-type: none;
    padding: 0;
}

.challenge-list li {
    margin: 5px 0;
}

.challenge-list a {
    text-decoration: none;
    color: #1976D2;
}

footer {
    background-color: #90CAF9;
    padding: 10px;
    text-align: center;
    color: #0D47A1;
}

@media (max-width: 600px) {
    .card-content {
        flex-direction: column;
        align-items: center;
    }

    .card-content img {
        max-width: 90%;
    }

    .card-content div {
        text-align: center;
    }
    .pdf-frame {
        width: 100%;
        height: 90vh;     /* ajusta a gusto */
        min-height: 600px;       /* Garantiza un mínimo en pantallas pequeñas */
        border: 1px solid #90CAF9;
        border-radius: 8px;
        background: #fff;
    }
}