BTW, that's the immediate downside of Bootstrap 3. You put the design back in the HTML instead of HTML. It would have been easier to define a div with a class and then in the CSS could have a way to define it's characteristics. In a way you can, but that makes things very complicated:
In your CSS you can do this:
Code:
@media(max-width:500px){
.thumb{
width: 100%;
}
}
@media(max-width:1024px){
.thumb{
width: 50%;
}
}
That would do about the same, you'll get a different CSS set for every screen size that way. Basically this is what Bootstrap does as well.