#cuerpo {width: 1350px;
        background: #33FFFF;
        font-size: 23px;
}
article {color: #000000;
    display: inline-block;
    margin: 0px 350px;
    font-size: 28px;
}
#Explicación { text-align: center;
            font-size: 35px;
            width: 1350px;
            height: 50px;
            display: inline-block;
            border: 2px solid #9933FF;
            color: #000000;
 }
#Actividad { text-align: left;
            width: 1350px;
            height: 700px;
            display: block;
            border: 2px solid #9933FF;
 }

.nivel { 
    border-radius: 10px;
    padding-bottom: initial;
    color: #0033FF;
    background-color: FFFFFF;
    width: 100px;
    height: 50px;
    margin: 50px 60px;
    font-size: 15px;
    display: inline-block;
}

#cabecera {background: #FFCCFF;
        padding: 10px;
        width: 1350px;
        height: 60px;
        border: 3px solid #9933FF;
}
img {width: 60px;
    display: inline-block;
}
h1{
    text-align: center;
    margin-right: 50px;
    margin-left: 50px;
    font-size: 30px;
    color: black;
}h2{
    text-align: left;
    font-size: 25px;
    color: blue;
    margin-left: 50px;
}