The problem is that each of the boxes has a width of 23.5%, but they also have a margin-left of 2%, which means if you put four boxes next to each other, the total width is (23.5% + 2%) x 4 = 102%, which causes the fourth box to wrap to the next line, because there’s only room for three.
The reason why the first line is able to hold four boxes is that the very first box has a class called clr_margin added to it, and there’s a CSS rule which sets margin-left to 0 for elements with that class. If you look closely at the second line, you will see that the first box on the second line is shifted over a little bit to the right, i.e., it’s not directly under the first box on the first line. That’s because it does not have that clr_margin class assigned to it, so it has a margin-left (spacing) of 2%. Because the first box on the second line is shifted over, there’s not enough room for the last box to fit on the same line.
The solution is to add a CSS rule which removes the margin-left from every fourth box past the first box (i.e., the 1st box, the 5th box, the 9th box, etc). Use a CSS plugin (unless the theme has a Custom CSS option) to add this rule:
@media (min-width: 768px) {
.home-blog-entry:nth-child(4n+1) {
margin-left: 0;
}
}
This should work no matter how many more boxes you add.