a {
    color: red;
    text-decoration: none;
}

nav {
    width: 100%;
}

nav .navbar-brand {
    text-transform: uppercase;
    font-weight: bold;
    color: white;
}

nav .navbar-brand:hover {
    color: white;
}

nav .nav-item .nav-link {
    text-transform: uppercase;
    color: white;
}

nav .nav-item .nav-link.active {
    font-weight: bold;
    color: white;
}

.navbar-expand-lg .navbar-nav {
    gap: 15px;
}

.navbar-collapse.show, .navbar-collapse.collapsing {
    background-color: black;
}

.navbar-toggler-icon {
    filter: brightness(100);
}

.header-image {
    background-color: black;
    text-align: center;
}

.header-image img {
    max-height: 400px;
}

.book-details {
    margin: 30px 0;
    display: flex;
    flex-direction: column;
}

.book-details img {
    max-width: 75%;
    align-self: center;
}

.book-details .subtitle {
    font-weight: bold;
    margin-top: 15px;
    font-size: 1em;
}
.book-details .buy-link {
    font-weight: bold;
}

footer.footer {
    background-color: black;
    display: flex;
    flex-direction: column;
    justify-content: center;
    color: white;
}

footer.footer .footer-links {
    display: flex;
    justify-content: center;
    gap: 30px;
}

footer.footer a {
    color: black;
    background-color: white;
    display: flex;
    width: 2.5em;
    height: 2.5em;
    border-radius: 2.5em;
    justify-content: center;
    align-items: center;
    line-height: unset;
    vertical-align: 0;
    text-decoration: none;
}

footer.footer a i {
    font-size: 1.5em;
}

footer.footer .copyright {
    font-size: 0.75em;
    padding: 30px 0;
}

@media (max-width: 767px) {
    header .navbar-expand-lg .navbar-nav {
        gap: 0px;
    }
}