Details that make TUI interfaces feel better

Great TUIs rarely come from a single thing. It's a collection of small details that compound into a professional experience. Apply these principles when building or reviewing Textual/terminal UI code.

Quick Reference

Category	When to Use
Layout	Alignment, spacing, responsive sizing, content regions
Color	Palette consistency, contrast, semantic color usage
Interaction	Focus management, key hints, modal flow, feedback
Typography	Text truncation, wrapping, Unicode, monospace alignment

Core Principles

1. Consistent Spacing

Use a spacing scale (1, 2, 4 cells). Mismatched padding between related elements is the most common thing that makes TUIs feel off. Textual's padding and margin CSS properties use cell units.

2. Optical Alignment Over Grid Alignment

When geometric centering looks wrong in a terminal, adjust optically. Asymmetric Unicode characters (arrows, bullets) and mixed-width content need manual nudging. A centered title above left-aligned content often needs 1 cell of left padding removed.

3. Color Hierarchy

Use 3-4 color tiers consistently:

• Primary: key actions, active focus (bright, saturated)
• Secondary: labels, metadata (dimmed)
• Muted: borders, separators (very dim)
• Danger/Success: semantic states only (red/green)

Never use bright colors for passive elements. Reserve saturation for things the user needs to notice.

4. Focus is Sacred

The focused widget must be visually distinct at a glance. Use border color changes, not just cursor position. A user glancing at the screen should instantly know where input will go.

5. Responsive Layout

TUI must work at 80x24 minimum. Use fr units and max-width/ min-width in Textual CSS to adapt. Content that overflows should truncate with ellipsis, never wrap into garbage.

6. Feedback on Every Action

Every keypress that does something should produce visible feedback within one frame. If an operation takes time, show a spinner or status message immediately — don't let the user wonder if their input was received.

7. Subtle Transitions

Textual supports CSS transitions. Use short durations (150-300ms) for background color and opacity changes on hover/focus. Never animate layout properties (width, height) — terminal reflow is not smooth.

8. Border Consistency

Pick one border style and stick with it. tall for primary containers, round for cards/modals, heavy for emphasis. Mixing ascii, tall, round, and heavy in one screen looks incoherent.

9. Key Hints

Always show available keys in a footer or status bar. Format as key action pairs separated by thin spaces. Dim the keys relative to the actions. Update hints contextually as focus moves.

10. Content Density

Terminal space is precious. Default to dense layouts. Use blank lines only to separate logical groups, never for decoration. Single-line headers over multi-line. Abbreviate labels when the full form is obvious from context.

Common Mistakes

Mistake	Fix
Inconsistent padding between similar widgets	Use a spacing constant
Bright colors on passive/decorative elements	Reserve bright for actions and focus
No visible focus indicator	Add border color or background change on focus
Content overflows and wraps badly	Set overflow: hidden with text-overflow: ellipsis
No key hints visible	Add contextual footer with available actions
Large empty regions at default size	Use fr units to distribute space
Mixed border styles in one view	Standardize on one style per element tier
No feedback on async operations	Show spinner/status immediately on action

Review Checklist

• Spacing is consistent between related elements
• Focused widget is visually distinct (border or background)
• Color usage follows the 3-4 tier hierarchy
• Layout works at 80x24 minimum terminal size
• Long text truncates with ellipsis, never wraps into garbage
• Key hints are visible and contextually updated
• Every user action produces visible feedback
• Border styles are consistent within each tier
• No bright colors on passive elements
• Transitions are short (150-300ms) and only on color/opacity

Reference Files

• layout.md — Alignment, spacing, responsive sizing
• color.md — Palette consistency, contrast, semantic usage
• interaction.md — Focus management, key hints, modals
• typography.md — Truncation, wrapping, Unicode alignment