I’m wondering why the home page and slider located here- https://colorlib.com/sparkling/ width is 100%. But the theme that I downloaded width was around 730px. I increased the size of my image to 1920 x 600 but it still doesn’t expand to 100%. I changed the width of the image to 100% but that didn’t work. I also change the width to width=“1920” height=“600” but that didn’t work either. Can someone tell me why this is happening?
Featured image size that are inside posts are 750px by 410px but the slider images are uncropped and displayed as-is. So if you upload 4000px by 1000px image it will be displayed in full size and also if you upload 100px by 100px it will be displayed in original size and won’t be scaled by using CSS or any other technique. Our recommended image size for slider is 1920px by 600px but you can feel free to use different size if you like.
Yes my image is 1920px by 600px. I even took one of the images from the sparkling theme and it’s doing the same thing.
Here’s an example of what it’s doing - Dropbox - notfullwidth.jpg - Simplify your life
We are talking about two completely different things here. You are not using slider but featured images for a page, that’s not the same thing.
Please read theme documentation: Sparkling Theme Documentation - Colorlib
And also this tutorial for featured images might be helpful: http://en.support.wordpress.com/featured-images/