## Fix ToC Scroll-Spy Highlighting Issue
### Problem
When clicking on a ToC link in the sidebar, the page scrolls to the
correct section, but the ToC highlights the *previous* section instead
of the current one. The correct section only gets highlighted after
scrolling down a few pixels.
### Root Cause
The `scrollspy` in `assets/js/common.js` was initialized without an
offset parameter, so it didn't account for the fixed navigation header
height (~56px).
### Solution
Added `offset: 100` parameter to the scrollspy initialization to
properly detect when a section becomes visible, accounting for the
header and some buffer space.
### Changes
- Modified `assets/js/common.js`: Added offset parameter to scrollspy
configuration
### Testing
- [x] ToC correctly highlights the current section immediately after
clicking
- [x] Headings remain visible (not hidden under header)
- [x] Smooth scrolling works as expected
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Co-authored-by: Maruan <alshedivat@users.noreply.github.com>
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