How match ID number with CSS regexp

I’m customising a WordPress theme and am stuck with the following CSS issue. I have a list of elements as follows:

li.block1, li.block2, li.block3, li.block4 {  top: 0; }
li.block5, li.block6, li.block7, li.block8 {  top: 150px; }
li.block9, li.block10, li.block11, li.block12 {  top: 300px; }

I’m generating the code using PHP and wish to use regexp to style these elements. I’d like to achieve the following:

- li.block[1-4] {style 1}
- li.block[5-9] {style 2}
- li.block[10-14] {style 3}
- and so on...

As I’m generating the li.block[number] dynamically based on user input, which could run into a few hundreds of elements, I believe that using regexp is the right way to go.

I’ve tried the following:

• Tried to use $ to match the last element, but I’d like some help on how to match on a range of values
• Tried using last-child attribute match, but as it’s dynamic, I can’t fix the last-child in advance
• Tried to use in-range to match the range, but I couldn’t figure out how to check whether the number is in the range
• and, several other DOM matching criteria using CSS

I think the CSS match condition I’m using is erroneous, so I’d like to request experts in this forum to show me how to properly use $ and range:

How do I use regexp based on: li.block[number,i, in range a-b] {Apply style number, i}?

I’m also open to other ideas that help me keep the theme dynamic.

Thanks in advance,
Mithun Sridharan