.video-container {  
    position: relative;  
    padding-bottom: 56.25%; /* Соотношение 16:9 */  
    height: 0;  
    overflow: hidden;  
}  

.video-container iframe {  
    position: absolute;  
    top: 0;  
    left: 0;  
    width: 100%;  
    height: 100%;  
}