Regex multiple lines search, matched, but highlighted only what initially is on screen

Question

Let's say I have the following fantasy code

// a long definition of a structure
struct long_struct {
    ...
};

There are tons of multiple lines inside such block of code. It cannot be displayed fully within a single page, but spans across multiple pages.

I would like to highlight all the lines inside such struct definition without highlighting struct long_struct { and };. I successfully did it with the following regex

/\(^struct\s\+long_struct\s*{\n\)\@<=\(^.*\n\)\{-}\(^};\)\@=

(in short such regex makes use of positive lookbehind, and positive lookahead, with non-greedy \{-} search.)

But the problem is that it will only highlights those lines that are able to be fit within a single page height. If I reduce the font size of terminal to fit more lines, it would be able to highlights additional lines as well. So I believe it's not the problem about above regex pattern.

How can I make vim able to highlight all those lines without limited by the number of lines shown on terminal screen?

Edit:

For a test case, you can use this file, then apply the same regex pattern above but for task_struct.