body{
    background-image:url(img/white.jpg);
    background-attachment: fixed;
    background-position: center center;
    background-size: cover;
}
:root {
    --fondo-base: #ffffff36;
    --fondo-hover: #8080809c;
    --borde: black;
    --borde-hover: white;
    --sombra: 0 2px 4px black;
    --sombra-hover: 0 2px 4px white;
}

div#menu-principal {
    width: 100%;
    background-color: var(--fondo-base);
    border: 1px outset var(--borde);
    box-shadow: var(--sombra);
    position: relative;
}

#menu-principal ul {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
}

#menu-principal ul li {
    position: relative;
}

#menu-principal ul li a {
    display: block;
    padding: 15px 20px;
    color: black;
    text-decoration: none;
    transition: all 0.3s ease;
}

#menu-principal ul li:hover > a {
    background-color: var(--fondo-hover);
    border: 1px outset var(--borde-hover);
    box-shadow: var(--sombra-hover);
}

.submenu {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background-color: var(--fondo-base);
    border: 1px outset var(--borde);
    box-shadow: var(--sombra);
    z-index: 100;
    flex-direction: column;
    min-width: 160px;
}

#menu-principal ul li:hover .submenu {
    display: block;
}

.submenu li {
    position: relative;
}

.submenu-nivel2 {
    display: none;
    position: absolute;
    top: 0;
    left: 100%;
    background-color: var(--fondo-base);
    border: 1px outset var(--borde);
    box-shadow: var(--sombra);
    min-width: 160px;
}

.submenu li:hover .submenu-nivel2 {
    display: block;
}