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

/* ===== Menú principal ===== */
.main-nav {
    margin-top: 10px;
    list-style: none;
    padding-left: 0;
    background-color: #13a4a4;
    display: flex;
    align-items: center;
}

.main-nav-item {
    border-right: 1px solid #ffffff;
}

.main-nav-item a,
.practicas summary {
    display: block;
    color: white;
    padding: 8px 12px;
    text-decoration: none;
    cursor: pointer;
}

.main-nav-item a:hover,
.practicas summary:hover {
    color: blue;
}

.main-nav-item a:active {
    color: chocolate;
}

/* ===== Menú desplegable ===== */
.practicas {
    position: relative;          /* referencia para el submenú */
}

.practicas summary {
    list-style: none;            /* quita la flechita por defecto */
}

.practicas summary::-webkit-details-marker {
    display: none;               /* quita la flechita en Chrome/Safari */
}

.practicas summary::after {
    content: " ▾";
}

.practicas[open] summary::after {
    content: " ▴";
}

.submenu {
    list-style: none;
    position: absolute;          /* flota sobre el contenido */
    top: 100%;
    left: 0;
    min-width: 260px;
    background-color: #13a4a4;
    border: 1px solid #ffffff;
    z-index: 10;
}

.submenu a:hover {
    background-color: #0e7a7a;
    color: white;
}

/* ===== Contenido ===== */
main {
    width: 98%;
    height: 500px;
    border: 10px solid grey;
}