* {
    box-sizing: border-box;
}

body {
    padding: 50px;
    background-color: rgb(229, 229, 229);
    font-family: Arial, Helvetica, sans-serif;
}

/* Header */
.header {
    padding: 1px;
    text-align: center;
    background-color: rgb(15, 32, 54);
    overflow: hidden;
}

.header h1 {
    font-size: 40px;
    color: white;
}

/* Main */
.main::after {
    content: "";
    display: table;
    clear: both;
}

/* Cards */
.card {
    background-color: white;
    width: 100%;
    padding: 20px;
    margin-top: 20px;
}

img {
    max-width: 100%;
}

/* Footer */
.footer {
    background-color: lightgray;
    text-align: center;
    margin-top: 20px;
    padding: 1px;
}

/* Responsive exceptions */
@media screen and (max-width: 800px) {

    .left,
    .right {
        width: 100%;
        padding: 0;
    }
}

@media screen and (max-width: 550px) {
    .nav a {
        float: none;
        width: 100%;
    }
}