Hi Sansar,
Thanks for writing in!
Unfortunately, that feature is not available in the theme, you need custom CSS to hide the header and sidebar . for the particular post.
The example CSS should look like this.
body.postid-10675 .masthead, body.postid-10675 aside.x-sidebar {
display: none !important;
}
body.postid-10675 .x-main {
width: 100% !important;
}
The post class should be found in the body.
If you would like to learn CSS, I am sharing few resources that you take a look to get started with CSS and an interesting tool that you can use to speed up the development process.
I recommend you to watch following video that will help you to get started with CSS.
https://www.youtube.com/watch?v=MFR4WXiLzpc
Sometimes it can get a bit difficult to find out the right selector to be able to write the required CSS codes. A handy tool that can help you in this is Google Chrome dev tools. I am sharing the resource that you can refer to get started with dev tools.
https://developers.google.com/web/tools/chrome-devtools/css/
https://developers.google.com/web/tools/chrome-devtools/
https://www.youtube.com/watch?v=tP_kXBJWPhQ&t=200s
Thanks.