Check out example codes for "responsive youtube video on a website". It will help you in understanding the concepts better.

Code Example 1

/*Add CSS*/
.container {
  position: relative;
  overflow: hidden;
  width: 100%;
  padding-top: 56.25%; /* 16:9 Aspect Ratio (divide 9 by 16 = 0.5625) */
}

/* Then style the iframe to fit in the container div with full height and width */
.responsive-iframe {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  width: 100%;
  height: 100%;
}

Code Example 2

//Add the following CSS to your code


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

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