40 lines
2.4 KiB
Markdown
40 lines
2.4 KiB
Markdown
---
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title: Smooth Scrolling in Agentic Chat Interfaces
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date: 2025-09-15
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coverImage:
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author: mariosant
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url: "/agentic-ui.png"
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---
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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:
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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.
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It sounds straightforward, but the implementation had a few subtle challenges.
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## The Core Challenge
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Most chat apps scroll new messages to the bottom, where they stack endlessly. For this interface, I wanted something more intentional:
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* The user’s own question should appear at the top of the viewport.
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* There should be extra breathing room below it so the agent’s reply flows in naturally.
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* That extra whitespace shouldn’t stick around forever - otherwise the layout starts looking broken.
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## Creating the Right Spacing
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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.
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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.
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## Knowing When to Remove It
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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.
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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.
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## Why This Matters
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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.
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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.
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