feat(ribbon): basic implementation for scroll pinning

apps/client/src/widgets/containers/content_header.css

@@ -0,0 +1,18 @@
+.content-header-widget {
+    position: relative;
+    transition: position 0.3s ease, box-shadow 0.3s ease, z-index 0.3s ease;
+    z-index: 8;
+}
+
+.content-header-widget.floating {
+    position: sticky;
+    top: 0;
+    z-index: 11;
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+    background-color: var(--main-background-color, #fff);
+}
+
+/* Ensure content inside doesn't get affected by the floating state */
+.content-header-widget > * {
+    transition: inherit;
+}

apps/client/src/widgets/containers/content_header.ts

@@ -2,6 +2,7 @@ import { EventData } from "../../components/app_context";
 import BasicWidget from "../basic_widget";
 import Container from "./container";
 import NoteContext from "../../components/note_context";
+import "./content_header.css";
 
 export default class ContentHeader extends Container<BasicWidget> {
 
@@ -11,6 +12,9 @@ export default class ContentHeader extends Container<BasicWidget> {
     resizeObserver: ResizeObserver;
     currentHeight: number = 0;
     currentSafeMargin: number = NaN;
+    previousScrollTop: number = 0;
+    isFloating: boolean = false;
+    scrollThreshold: number = 10; // pixels before triggering float
 
     constructor() {
         super();
@@ -35,7 +39,36 @@ export default class ContentHeader extends Container<BasicWidget> {
         this.thisElement = this.$widget.get(0)!;
 
         this.resizeObserver.observe(this.thisElement);
-        this.parentElement.addEventListener("scroll", this.updateSafeMargin.bind(this));
+        this.parentElement.addEventListener("scroll", this.updateScrollState.bind(this), { passive: true });
+    }
+
+    updateScrollState() {
+        const currentScrollTop = this.parentElement!.scrollTop;
+        const isScrollingUp = currentScrollTop < this.previousScrollTop;
+        const hasMovedEnough = Math.abs(currentScrollTop - this.previousScrollTop) > this.scrollThreshold;
+
+        if (hasMovedEnough) {
+            this.setFloating(isScrollingUp);
+            this.previousScrollTop = currentScrollTop;
+        }
+
+        this.updateSafeMargin();
+    }
+
+    setFloating(shouldFloat: boolean) {
+        if (shouldFloat !== this.isFloating) {
+            this.isFloating = shouldFloat;
+
+            if (shouldFloat) {
+                this.$widget.addClass("floating");
+                // Set CSS variable so ribbon can position itself below the floating header
+                this.parentElement!.style.setProperty("--content-header-height", `${this.currentHeight}px`);
+            } else {
+                this.$widget.removeClass("floating");
+                // Reset CSS variable when header is not floating
+                this.parentElement!.style.removeProperty("--content-header-height");
+            }
+        }
     }
 
     updateSafeMargin() {

apps/client/src/widgets/ribbon/style.css

@@ -1,5 +1,15 @@
 .ribbon-container {
     margin-bottom: 5px;
+    position: relative;
+    transition: position 0.3s ease, z-index 0.3s ease, top 0.3s ease;
+    z-index: 8;
+}
+
+/* When content header is floating, ribbon sticks below it */
+.scrolling-container:has(.content-header-widget.floating) .ribbon-container {
+    position: sticky;
+    top: var(--content-header-height, 100px);
+    z-index: 10;
 }
 
 .ribbon-top-row {