.embed-container {
    position: relative;
    padding-bottom: 56.25%;
    height: 0;
    overflow: hidden;
}
.embed-container iframe {
    position: absolute;
    top:0;
    left: 0;
    width: 100%;
    height: 100%;
}

/* CSS general */
.mi-iframe {
    width: 100px;
    height: 50px;
  }
  
  /* CSS pantallas de 320px o superior */
  @media (min-width: 320px) {
  
    .mi-iframe {
      width: 200px;
      height: 150px;
    } 
  
  }
  
  /* CSS pantalla 768px o superior */
  @media (min-width: 768px) {
  
    .mi-iframe {
      width: 500px;
      height: 350px;
    } 
  
  }