.stripy tr:nth-child(4n+1){
background-color: grey;
}
.stripy tr:nth-child(4n+2){
background-color: grey;
}<table class="stripy">
body {
color: #8f8f8f;
font: 12px Tahoma, sans-serif;
background-color: #f8f8f8;
margin: 0;
padding: 0;
}
header,
nav,
section,
article,
aside,
footer {
display: block;
}
#wrapper {
min-width: 1024px;
max-width: 98%;
position:absolute;
height: 100%;
}
aside {
float: left;
width: 250px;
position:absolute;
background: #272727;
height: 100%;
}
section {
margin-left: 280px;
margin-right: 0px;
}