fixed scrollspy

site/src/jsMain/kotlin/DocsPage.kt

@@ -181,7 +181,7 @@ fun DocsPage(
             scheduled = false
             try {
                 val heads = toc.mapNotNull { id -> el.querySelector("#${id.id}") as? HTMLHeadingElement }
-                val tops = heads.map { it.getBoundingClientRect().top + window.scrollY }
+                val tops = heads.map { it.getBoundingClientRect().top }
                 val offset = (updateNavbarOffsetVar() + 16).toDouble()
                 val idx = activeIndexForTops(tops, offset)
                 setActiveTocId(if (idx in toc.indices) toc[idx].id else null)

site/src/jsMain/kotlin/Main.kt

@@ -1024,11 +1024,15 @@ internal fun normalizePath(path: String): String {
 // If none are above the offset, returns 0. If list is empty, returns 0.
 fun activeIndexForTops(tops: List<Double>, offsetPx: Double): Int {
     if (tops.isEmpty()) return 0
+    var lastAbove = 0
     for (i in tops.indices) {
-        if (tops[i] - offsetPx > 0.0) return i
+        if (tops[i] <= offsetPx) {
+            lastAbove = i
+        } else {
+            break
         }
-    // If all headings are above the offset, select the last one
+    }
-    return tops.size - 1
+    return lastAbove
 }
 
 fun main() {

site/src/jsTest/kotlin/ScrollSpyTest.kt

@@ -28,20 +28,20 @@ class ScrollSpyTest {
     fun selectsFirstWhenOnlyFirstIsAboveOffset() {
         val tops = listOf(20.0, 200.0, 800.0) // px from viewport top
         val idx = activeIndexForTops(tops, offsetPx = 80.0)
-        assertEquals(1, idx) // 20 <= 80, 200 > 80 -> index 1 (second heading is first below offset)
+        assertEquals(0, idx) // 20 <= 80 (active), 200 > 80 (stops) -> index 0
     }
 
     @Test
     fun selectsLastHeadingAboveOffset() {
         val tops = listOf(-100.0, 50.0, 70.0)
         val idx = activeIndexForTops(tops, offsetPx = 80.0)
-        assertEquals(2, idx) // all three are <= 80 -> last index
+        assertEquals(2, idx) // all three are <= 80 -> last index 2
     }
 
     @Test
     fun stopsBeforeFirstBelowOffset() {
         val tops = listOf(-200.0, -50.0, 30.0, 150.0, 400.0)
         val idx = activeIndexForTops(tops, offsetPx = 80.0)
-        assertEquals(3, idx) // 30 <= 80 qualifies; 150 > 80 stops, so index 3rd (0-based -> 3?)
+        assertEquals(2, idx) // 30 <= 80 is the last one; 150 > 80 -> index 2
     }
 }