* {
    box-sizing: border-box;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background-color: white;
    margin: 0px;
}

div {
    padding: 10px;
}

header {
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: #43a047;
    
    height: 140px;
}

main {
    margin: 0px;
    background-color: white;
    width: auto;
}

.navbar {
    display: flex;
    justify-content: center;
    background-color: #068541;
}

.navbar ul {
    list-style: none;
    background-color: #068541;
    padding: 0px;
    margin: 0px;
    overflow: hidden;
}

.navbar a {
    color: yellow;
    text-decoration: none;
    padding: 15px;
    display: block;
    text-align: center;
}

.navbar a:hover {
    background-color: #fcb900;
    color: black;
}

.navbar li {
    float: left;
}

aside {
    width: 30%;
    float: left;
    padding: 10px;
}

section {
    width: 70%;
    float: left;
    padding: 10px;
}

article {
    width: 30%;
    float: left;
    padding: 10px;
}

footer {
    display: block;
    clear: both;
    text-align: center;
    align-items: center;
    justify-content: center;
    color: yellow;
    background-color: #43a047;
    padding: 20px;
}

.book {
    display: flex;
    align-items: top;
    gap: 20px;
    border-style: solid;
    border-width: 3px;
    border-color: #04a550;
}

.round-link-button {
    background-color: #fcb900;
    border: none;
    color: black;
    padding: 15px 30px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 16px;
    margin: 4px 2px;
    cursor: pointer;
    border-radius: 15px;
    box-sizing: border-box;
}


@media screen and (max-width: 600px) {
    aside,section,article{
        width: 100%;
    }
}