Hello @technicaljayendra
I don’t know that oceanwp theme, and the reason why the videos are not resizing is because they use the youtube iframe that includes the width and height attribute. They then have had to write the fitvidz script behind it to over ride the width and height attribute for auto resize.
There is actually no need for that at all. WordPress Oembed auto resizes the videos. I have made a demo to to show you what I mean by that. This is on the WordPress 5.3.2 – with the default 2019 Theme – your first 3 videos and a3 Lazy Load.
When you check it in different size screens you will see that the first 2 videos added by the Gutenberg Video block and just copy and paste the video url into the post auto resize in all devices. The third one which is added by the Youtube embed code does not resize in devices – because the width and height attributes are specified.
To fix the issue on your page – if you are using the Gutenberg editor – you can just use the Youtube Video block and copy and paste the video url in the box provided or you can just use a paragraph block and copy / paste the video url.
If you are using the classic editor – just copy and paste the video url into the post / page.
Here is the link to the demo for you to check that.
