Here’s a test site (10,000 pages) we used during some performance improvements on the internal pagination template:
git clone --single-branch -b hugo-github-issue-8602 https://github.com/jmooring/hugo-testing hugo-github-issue-8602
cd hugo-github-issue-8602
hugo server
And the lighthouse results:
Related to width… by default there are as many as 9 buttons (first, prev, slots 1-5, next, last). But there’s an undocumented, alternate format that reduces that to a maximum of 7 buttons (first, prev, slots 1-3, next, last). Details here:
https://github.com/gohugoio/hugo/pull/8602#issue-908705409
Related to styling… the structure and class names are, I think, standard (if such a thing exists). For example, out of the box with Bootstrap it looks and works as expected.
The test site that I referenced above includes some CSS for the nav; perhaps there’s something useful in there for you.