header, section, footer {
    width: 1200px;
    margin-left: auto;
    margin-right: auto;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
}
*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
header {
    height: 200px;
    background-color: rgb(19, 18, 18);
}
nav {
    width: 500px;
    margin-right: 50px;
    margin-top: 90px;
    font-size: 30px;
    float: right;
    text-align: center;
}
.menu-horizontal {
    list-style: none;
    display: flex;
    justify-content: space-around;
}
.menu-horizontal > li > a {
    display: block;
    padding: 15px 20px;
    color: darkorange;
    text-decoration: none;
}
.menu-horizontal > li > a:hover {
    background-color: rgb(90, 89, 89);
    width: 190px;
}
.menu-vertical {
    display: none;
    list-style: none;
    width: 190px;
    background-color: rgb(19, 18, 18);
    text-align: center;
    position: absolute;
}
.menu-horizontal > li:hover .menu-vertical {
    display: block;
}
.menu-vertical li :hover {
    background-color: rgb(90, 89, 89);
}
.menu-vertical li a {
    display: block;
    color: darkorange;
    padding: 15px 15px 15px 20px;
    text-decoration: none;
}
#h_b2 {
    height: 180px;
    width: 440px;
    float: left;
    background-image: url(imagenes/logo-imagen.gif);
    background-size: cover;
    margin-top: 10px;
    margin-left: 40px;
}
section {
    height: 5100px;
    background-color: rgb(19, 18, 18);
    padding-top: 20px;
}
#s-b1 {
    height: 580px;
    width: 440px;
    float: right;
    background-image: url(imagenes/obra1-imagen.jpg);
    background-size: cover;
    margin-right: 20px;
}
#s-b2 {
    height: 300px;
    width: 600px;
    float: left;
    margin-top: 100px;
    margin-left: 20px;
}
section div p {
    text-align: center;
    font-size: 20px;
    color: white;
    margin-top: 20px;
}
h1 {
    text-align: center;
    color: white;
    margin-top: 10px;
}
#s-b3 {
    height: 430px;
    width: 620px;
    float: left;
    background-image: url(imagenes/obra2-imagen.jpg);
    background-size: cover;
    margin-left: 20px;
    margin-top: 280px;
}
#s-b4 {
    height: 300px;
    width: 500px;
    float: right;
    margin-top: 150px;
    margin-right: 20px;
}
#s-b5 {
    height: 400px;
    width: 610px;
    float: right;
    background-image: url(imagenes/obra3-imagen.jpg);
    background-size: cover;
    margin-right: 20px;
    margin-top: 100px;
}
#s-b6 {
    height: 300px;
    width: 500px;
    float: left;
    margin-top: 150px;
    margin-left: 20px;
}
#s-b7 {
    height: 510px;
    width: 530px;
    float: left;
    background-image: url(imagenes/obra4-imagen.jpg);
    background-size: cover;
    margin-left: 20px;
    margin-top: 100px;
}
#s-b8 {
    height: 300px;
    width: 500px;
    float: right;
    margin-top: 150px;
    margin-right: 20px;
}
#s-b9 {
    height: 580px;
    width: 440px;
    float: right;
    background-image: url(imagenes/obra5-imagen.jpg);
    background-size: cover;
    margin-right: 20px;
    margin-top: 170px;
}
#s-b10 {
    height: 300px;
    width: 500px;
    float: left;
    margin-top: 170px;
    margin-left: 20px;
}
#s-b11 {
    height: 480px;
    width: 530px;
    float: left;
    background-image: url(imagenes/obra6-imagen.jpg);
    background-size: cover;
    margin-left: 20px;
    margin-top: 220px;
}
#s-b12 {
    height: 300px;
    width: 500px;
    float: right;
    margin-top: 120px;
    margin-right: 20px;
}
#s-b13 {
    height: 470px;
    width: 530px;
    float: right;
    background-image: url(imagenes/obra7-imagen.jpg);
    background-size: cover;
    margin-right: 20px;
    margin-top: 220px;
}
#s-b14 {
    height: 300px;
    width: 500px;
    float: left;
    margin-top: 170px;
    margin-left: 20px;
}
#s-b15 {
    height: 410px;
    width: 600px;
    float: left;
    background-image: url(imagenes/obra8-imagen.jpg);
    background-size: cover;
    margin-left: 20px;
    margin-top: 220px;
}
#s-b16 {
    height: 300px;
    width: 500px;
    float: right;
    margin-top: 170px;
    margin-right: 20px;
}
#s-b17 {
    height: 420px;
    width: 570px;
    float: right;
    background-image: url(imagenes/obra9-imagen.jpg);
    background-size: cover;
    margin-right: 20px;
    margin-top: 120px;
}
#s-b18 {
    height: 300px;
    width: 500px;
    float: left;
    margin-top: 170px;
    margin-left: 20px;
}
footer {
    height: 150px;
    background-color: rgb(19, 18, 18);
}
#f_b1 {
    height: 90px;
    width: 300px;
    float: left;
    margin-top: 25px;
    margin-left: 10px;
}
#f_b2 {
    height: 90px;
    width: 300px;
    float: left;
    margin-top: 25px;
    margin-left: 60px;
}
#f_b3 {
    height: 90px;
    width: 300px;
    float: right;
    margin-top: 25px;
    margin-right: 60px;
}
.letras {
    color: darkorange;
    font-size: 20px;
    font-weight: 50px;
    text-align: center;
    padding: 5px;
}
h2 {
    text-align: center;
    color: white;
}

@media all and (max-width: 570px) {
    header, section, footer {
        width: 100%;
    }
    header {
        height: auto;
    }
    nav {
        width: 100%;
        margin-right: 0;
        margin-top: 0;
        font-size: 20px;
        float: none;
    }
    .menu-vertical {
        width: 100%;
        position: relative;
    }
    #h_b2 {
        height: 180px;
        width: 100%;
        float: none;
        background-image: url(imagenes/logo-imagen.gif);
        margin-top: 0;
        margin-left: 0;
    }
    section {
        height: auto;
    }
    #s-b1 {
        height: 550px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra1-imagen.jpg);
        margin-right: 0;
    }
    #s-b2 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #s-b3 {
        height: 290px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra2-imagen.jpg);
        margin-left: 0;
        margin-top: 80px;
    }
    #s-b4 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-right: 0;
    }
    #s-b5 {
        height: 260px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra3-imagen.jpg);
        margin-right: 0;
        margin-top: 80px;
    }
    #s-b6 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #s-b7 {
        height: 400px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra4-imagen.jpg);
        margin-left: 0;
        margin-top: 80px;
    }
    #s-b8 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-right: 0;
    }
    #s-b9 {
        height: 550px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra5-imagen.jpg);
        margin-right: 0;
        margin-top: 80px;
    }
    #s-b10 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #s-b11 {
        height: 380px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra6-imagen.jpg);
        margin-left: 0;
        margin-top: 80px;
    }
    #s-b12 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-right: 0;
    }
    #s-b13 {
        height: 365px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra7-imagen.jpg);
        margin-right: 0;
        margin-top: 80px;
    }
    #s-b14 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #s-b15 {
        height: 290px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra8-imagen.jpg);
        margin-left: 0;
        margin-top: 80px;
    }
    #s-b16 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-right: 0;
    }
    #s-b17 {
        height: 300px;
        width: 100%;
        float: none;
        background-image: url(imagenes/obra9-imagen.jpg); 
        margin-right: 0;
        margin-top: 80px;
    }
    #s-b18 {
        height: auto;
        width: 100%;
        float: left;
        margin-top: 0;
        margin-left: 0;
        padding-bottom: 80px;
    }
    footer {
        height: auto;
    }
    #f_b1 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #f_b2 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-left: 0;
    }
    #f_b3 {
        height: auto;
        width: 100%;
        float: none;
        margin-top: 0;
        margin-right: 0;
    }
}