@media(max-width:600px){
.mod-sampleBlock .mod-sampleBlock-image {
float:none;
margin:0 10px;
}
.mod-sampleBlock .mod-sampleBlock-image img{margin:0 auto;}
}
書き方参考
http://webdesignerwork.jp/web/responsivewebdesign/
http://yomotsu.net/blog/2012/10/01/mediaquery-goodpractice.html