Agentic UI scrolling

content/articles/2025-09-15-smooth-scrolling.md

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+---
+title: Smooth Scrolling in Agentic Chat Interfaces
+date: 2025-09-15
+coverImage:
+  author: mariosant
+  url: "/agentic-ui.png"
+---
+
+When building conversational UIs, small interaction details can make a huge difference in how natural the experience feels. Recently, while working on an agentic chat interface, I ran into a deceptively simple requirement:
+
+Whenever the user submits a question, the viewport should scroll to that question, position it neatly at the top, and then let the user read the agent’s response at their own pace.
+
+It sounds straightforward, but the implementation had a few subtle challenges.
+
+## The Core Challenge
+
+Most chat apps scroll new messages to the bottom, where they stack endlessly. For this interface, I wanted something more intentional:
+
+* The user’s own question should appear at the top of the viewport.
+* There should be extra breathing room below it so the agent’s reply flows in naturally.
+* That extra whitespace shouldn’t stick around forever - otherwise the layout starts looking broken.
+
+## Creating the Right Spacing
+
+To achieve the temporary space effect, I leaned on modern CSS units like viewport height (vh) and dynamic CSS variables. The idea was simple: whenever the user sends a question, create some space at the bottom of the chat, which effectively pushes their question to the top of the screen.
+
+From a user perspective, this feels intentional: their message takes center stage, while the agent’s answer appears in a comfortable, readable position just below.
+
+## Knowing When to Remove It
+
+The real trick was deciding when to get rid of that artificial space. Leaving it there permanently made the UI look odd, as if something was missing below the messages.
+
+This is where the Intersection Observer API came into play. By watching a small invisible element placed in that whitespace, the system could detect when the user scrolled and the space was no longer visible. At that moment, the extra space was removed - restoring the chat to a normal flow.
+
+## Why This Matters
+
+This kind of interaction is easy to overlook, but it shapes how people experience a conversational product. Instead of feeling like a chat feed bolted onto a webpage, the interface feels deliberate and respectful of the user’s focus.
+
+By combining viewport-relative layout techniques with scroll-aware cleanup logic, I was able to create a chat UI that feels smooth, intentional, and more human.