:root {
    --primary-color: #002855;
    --secondary-color: #42a5f5;
    --tertiary-color: #bcd4e6;
    --background-color: #e3f2fd;
}
html {
    box-sizing: border-box;
}
*, *:before, *:after {
    box-sizing: inherit;
}

body {
    font-family: Arial, sans-serif;
    margin: 0 auto;
    padding: 0;
    max-width: 1200px;
    background-color: var(--background-color);
}

@media (max-width: 900px) {
    body {
        width: 100%;
    }
}

a {
    text-decoration: none;
    color: var(--primary-color);
}

h1, h2, h3 {
    color: var(--primary-color);
}

h1, h2 {
    margin-top: 0;
    margin-bottom: 0.5em;
}

header {
    color: white;
    padding: 1em;
    text-align: center;
}

header nav {
    position: relative;
    background-color: var(--primary-color);
}

header nav .nav-links {
    height: 3em;
    display: flex;
    justify-content: space-evenly;
    align-items: center;
}

header nav a {
    font-weight: bold;
    align-content: center;
    color: var(--background-color);
    padding: 0 1em;
    height: 100%;
}

header nav a.active, header nav a:hover {
    background-color: var(--secondary-color);
    color: var(--primary-color);
}

header nav .mobile-nav, header nav #nav-check {
    display: none;
}

@media (max-width: 900px) {
    header {
        padding: 0;
    }

    header > a {
        display: none;
    }

    header nav {
        display: flex;
        flex-direction: column;
    }

    header nav .mobile-nav {
        display: flex;
        width: 100%;
        justify-content: space-between;
        height: 4em;
    }

    header nav a {
        height: 3em;
    }

    header nav .nav-title {
        align-self: center;
        padding-left: 1em;
    }

    header nav .nav-title a:hover {
        background-color: transparent;
    }

    header nav .nav-title h1 {
        margin-bottom: 0;
        color: #FFF;
    }

    header nav .nav-btn {
        display: inline-block;
    }

    header nav .nav-btn > label:hover, nav #nav-check:checked ~ .nav-btn > label {
        background-color: var(--secondary-color);
    }

    header nav .nav-btn > label {
        display: flex;
        justify-content: center;
        align-items: center;
        position: relative;
        padding: 0 1em;
        height: 100%;
    }

    header nav .nav-btn > label:before {
        display: block;
        font-size: 2em;
        content: "\2630";
    }

    header nav > .nav-links {
        position: absolute;
        display: block;
        width: 100%;
        background-color: var(--primary-color);
        height: 0;
        transition: all 0.3s ease-in;
        overflow-y: hidden;
        top: 4em;
        left: 0;
    }

    header nav .nav-links > a {
        display: block;
        width: 100%;
    }

    header nav #nav-check:not(:checked) ~ .nav-links {
        height: 0;
    }

    header nav #nav-check:checked ~ .nav-links {
        height: calc(100vh - 50px);
        overflow-y: auto;
    }
}

section {
    width: 100%;
    display: flex;
    gap: 1em;
    padding: 1em;
}

section p {
    line-height: 1.5em;
}

section p:first-child {
    margin-top: 0;
}

.img-container {
    max-width: 40%;
    flex-shrink: 0;
    display: flex;
    flex-direction: column;
    gap: 0.5em;
    align-items: center;
}

.img-container * {
    width: 100%;
}

.book {
    width: 100%;
    display: flex;
    gap: 1em;
}

@media (max-width: 900px) {
    section {
        padding: 0;
        flex-direction: column-reverse;
    }

    section img {
        max-height: 30%;
    }

    .content {
        width: 100%;
        padding: 1em;
    }

    .img-container {
        max-width: 100%;
    }

    .book {
        flex-direction: column;
        align-items: center;
    }

    .book img {
        max-width: 75%;
    }
}

footer {
    display: flex;
    justify-content: space-around;
    padding: 1em;
}

footer h2 {
    margin-top: 0.5em;
}

footer p {
    margin-top: 0.5em;
    margin-bottom: 0.5em;
}

footer a {
    color: var(--primary-color);
}

footer > div {
    display: flex;
    flex-direction: column;
    background-color: var(--tertiary-color);
    padding: 0 1em;
    width: 25%;
}

footer a {
    display: block;
}

footer img {
    width: 100%;
    max-width: 75%;
}

@media (max-width: 900px) {
    footer {
        flex-direction: column;
    }

    footer > div {
        width: 100%;
        padding: 1em;
    }

    footer img {
        max-width: 100%;
    }
}