main {
    width: 95%;
    margin: 0 auto;
}

html, body {
background-color: #ffffff;
}

body {
margin: 0;
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
font-size: 13px;
font-weight: normal;
color: #404040;
}

h1 {
font-size: 300%;
margin: 0;
padding: 0;
}

h1, h2{
text-align: center;
text-transform: uppercase;
}

/*添加下面的代码*/
@media (min-width:700px){
    .column {
        width:30%;
        display: inline-block;
        margin-left: 2%;
        /*border: 1px dashed black;*/
    } 
}

/*Write a media query that changes the background color of the screen
     from red, to blue, to green as the screen gets larger.*/
@media screen {
    body{
        background-color:#f00;
    }
}


@media screen and (min-width:700px){
    body{
        background-color:#00f;
    }
}


@media screen and (min-width:1000px){
    body{
        background-color:#0f0;
    }
}