Changing the Image width

The images in the widget are very small

If I change the width from Simple Instagram options , the images deteriorate “-pixelated-
To change this, I followed these instructions: (but nothing change)

On your dashboard, go to appearance->editor in the menu on the left-hand side. On the resulting page, look in the list of files on the right-hand side and click on the one that says “Stylesheet (style.css)”. This is your stylesheet, and determines how your site looks. We’ll add a new rule that’ll override how the instagram widget looks.

Scroll to the bottom of the file and add the following text:

.si_feed_widget .si_item{
  width: 100%;
}

Then click on the Update File button. If you go to your homepage and refresh, you’ll notice that the images are now one-per-row.

Thank for your help.
Ariel

https://wordpress.org/plugins/simple-instagram/