body{
    font-size 90%;
    background-image: url("http://wallpaperspics.com/thumbs/26/7/wallpapers-desktop-background-blue-cube-web-262967.jpg");
    background-attachment: fixed;
    background-position: center center;
    text-align: center;
    padding-top: 2cm;
    background-size: cover;
    background-repeat: no-repeat;
}
header{
    width: 75%;
    color: lime;
    margin: 0 auto;
    opacity: 1;
    text-align: center;
    font-family: Times New Roman;
    font-weight: normal;
}
h1{
    font-size: 3em;
    color: lime;
}
h2{
    font-size: 1.5em;
    color: green;
}
p{
    color: lime;
}
div {
    position: center;
    display: inline-block;
    float: center;
}
div.t1 {
    opacity: .7;
    width: 15em;
    height: 30em;
    margin: 1em;
    border: none;
    padding: 1em 1em;
    text-align: justify;
    color: lime;
    background-color: gray;
}
div.t2 { 
    opacity: .7;
    width: 15em;
    height: 30em;
    margin: 1em;
    border: none;
    padding: 1em 1em;
    text-align: justify;
     color: lime;
    background-color: gray;
 }
div.t3 { 
    opacity: .7;
    width: 15em;
    height: 30em;
    margin: 1em;
    border: none;
    padding: 1em 1em;
    text-align: justify;
     color: lime;
    background-color: gray;
 }
div.t4 {
    opacity: .7;
    width: 15em;
    height: 30em;
    margin: 1em;
    border:none;
    padding: 1em 1em;
    text-align: justify;
     color: lime;
    background-color: gray;
 }
div.t5 {
    opacity: .7;
    width: 15em;
    height: 30em;
    margin: 1em;
    border: none;
    padding: 1em 1em;
    text-align: justify;
     color: lime;
    background-color: gray;
 }