layout home page changed

I am using Mystile theme. A few days ago, my home page shows 4 thumbnail pictures in a row. But now, my site shows just 2 thumbnail pictures in a row. What should i do to fix it. I’ve change in custom.css but i cant find where is the trouble.

The below pictures is the different cases on my site. You can see my site on https://solobaju.com. Thank you so much.
Before: https://i1232.photobucket.com/albums/ff362/meziaz/MyBlogbefore_zps7439708f.jpg
After: https://i1232.photobucket.com/albums/ff362/meziaz/myblogafter_zpsa922c278.jpg