media query

CSS
@media only screen and (max-width: 600px) {
  body {
    background-color: lightblue;
  }
}@media (max-height : 800px){ /* from 0 to 800 px max height applies */
  p{
    font-size:10px
  }
}@media only screen and (max-width: 600px) {
  .class {
    // Your CSS
  }
}
Source

Also in CSS: