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

body {
    background-color: #f0f0f0;
    font-family: Arial, sans-serif;
    color: #333;
}

.wrapper {
    margin: 20px auto;
    width: 960px;
    background-color: #fff;
    overflow: hidden;
}

#header, #footer {
    padding: 20px;
    text-align: center;
    background-color: #e2e2e2;
}

#main-content {
    padding: 10px;
    overflow: hidden;
}

.box {
    float: left;
    width: 285px;
    margin: 10px;
    padding: 15px;
    border: 1px solid #ddd;
    background-color: #fff;
    min-height: 450px;
}

.box img {
    width: 100%;
    height: auto;
    display: block;
    margin-bottom: 10px;
    background-color: #ccc;
}

.box h3 {
    margin: 10px 0;
    font-size: 1.1em;
}

@media screen and (max-width: 960px) {
    .wrapper {
        width: 640px;
    }
}

@media screen and (max-width: 640px) {
    .wrapper {
        width: 320px;
    }
    
    .box {
        width: 290px;
        margin: 10px auto;
        float: none;
    }

    h1 {
        font-size: 1.4em;
    }
}