So this tutorial will show you how to increase the thumbnail resolution size of the popular posts Blogger widget, even though we can apply this trick on any of the blog widgets.
Changing the Thumbnail Size for the Popular Posts Widget
Step 1. First, let's add the Popular posts gadget by going to "Layout" > click on the "Add a gadget" link and select "Popular Posts" from the popup window.Step 2. Next, go to "Template" > click on the "Edit HTML" button > click anywhere inside the code area to open the Blogger search box using the CTRL + F keys.
Step 3. Type or paste the following tag inside the search box then hit Enter to find it:
After you found the tag, add this CSS above it:
Step 4. Now search for this tag: