@media only screen and (max-width:800px){
#block1{width:20%}
#block2{width:40%}
#block3{width:40%}
}
@media only screen and (max-width:600px){
#block1{width:20%}
#block2{width:20%}
#block3{width:60%}
}
@media only screen and (max-width:400px){
#block1{width:33%}
#block2{width:33%}
#block3{width:33%}
}