version: "1.0.1" name: matlab-uihtml-design description: Generate beautiful, distinctive HTML/CSS/JS control panels for MATLAB uihtml components. 8 built-in styles (Clean, Material, Cosmic Dark, Neumorphic, Dashboard Light, Midnight Gradient, Minimal Mono, Warm Dark) plus custom aesthetics. Produces production-grade UI with sliders, buttons, toggles, and panels. Use when building visually polished MATLAB app UIs with uihtml. license: MathWorks BSD-3-Clause (see LICENSE) metadata: author: MathWorks version: "1.0"

MATLAB uihtml Design Skill

Generate production-grade HTML/CSS/JS control panels for MATLAB uihtml components with distinctive, configurable visual styles.

When to Use

• User wants beautiful custom controls in a MATLAB app via uihtml
• User asks for a specific design style (Clean, Material, dark theme, etc.)
• User wants to redesign or restyle existing uihtml controls
• User describes a custom aesthetic for their MATLAB app controls

Style Selection

Built-in styles are documented in references/design-styles.md. To apply a style:

1. If the user names a built-in style, read the corresponding file from references/styles/<name>.md
2. If the user describes a custom aesthetic, apply creative design thinking (see below) without loading a reference style
3. If no style is specified, open the visual style gallery in the user's browser so they can see all 8 styles side-by-side:

``bash start "" "<skill-directory>/assets/style-gallery.html" # Windows open "<skill-directory>/assets/style-gallery.html" # macOS ``

Then ask: "I've opened the style gallery in your browser. Which style would you like? You can also describe a custom aesthetic."

The gallery shows interactive previews of all 8 built-in styles with a Dark/Light toggle. The available styles are:

If the user says "just pick one" or wants to move fast, default to Clean.

Each style reference follows the 9-section DESIGN.md format and provides complete specifications for colors, typography, components, motion, and guardrails.

Design Thinking

Before generating code, commit to a clear aesthetic direction:

• Purpose: What does this control panel do? Who uses it?
• Tone: What feeling should the interface evoke?
• Constraints: Container size, MATLAB integration requirements, offline (no CDN)
• Differentiation: What makes this memorable and cohesive?

Execute the chosen direction with precision. Bold maximalism and refined minimalism both work, as long as the choice is intentional.

Workflow

1. Style selection: Identify or create the aesthetic direction
2. Component planning: Determine which controls are needed (sliders, buttons, toggles, etc.)
3. HTML generation: Produce self-contained HTML with the chosen style applied
4. MATLAB integration: Include setup(htmlComponent) boilerplate; defer full MATLAB-side wiring to the matlab-uihtml-app-builder skill

Component Library (v1)

Sliders

• Range inputs with custom thumb and track styling
• Value display with formatted units
• Horizontal layout with label + value header

Buttons

• Primary/Filled: Bold accent color, prominent shadow/glow
• Secondary/Outlined: Transparent with border, subtle hover
• Destructive/Danger: Warning color for stop/reset actions
• State: default, hover, focus-visible, active (scale 0.97), disabled (see the Interactive states table in Design Guardrails)

Toggles

• Sliding toggle switches
• On/off states with color transition
• Keyboard-operable (focusable, toggle on Space/Enter) with accessible click/tap targets

Theme System

All styles use CSS custom properties for theming. The base architecture:

:root {
    /* Semantic colors, filled by chosen style */
    --color-bg-primary: ...;
    --color-bg-secondary: ...;
    --color-bg-surface: ...;
    --color-accent: ...;
    --color-accent-hover: ...;
    --color-text-primary: ...;
    --color-text-secondary: ...;
    --color-border: ...;
 
    /* Spacing */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;
 
    /* Typography */
    --font-family: ...;
    --font-size-sm: ...;
    --font-size-md: ...;
    --font-size-lg: ...;
 
    /* Radii & Shadows */
    --radius-sm: ...;
    --radius-md: ...;
    --shadow-sm: ...;
    --shadow-md: ...;
 
    /* Motion */
    --transition-fast: ...;
    --transition-med: ...;
}

Support both light and dark modes via prefers-color-scheme media query or a data-theme attribute on <html>:

@media (prefers-color-scheme: dark) { ... }
/* or */
[data-theme="dark"] { ... }

Container-Aware Spacing

uihtml containers in MATLAB apps are often height-constrained (e.g., a narrow side panel). When applying any style:

• Read the existing HTML first to understand how many controls need to fit
• Prioritize fitting all controls over matching the style's ideal spacing. Reduce padding, gaps, and font sizes as needed; the neumorphic effect still works at 16px padding and 16px gaps
• Use compact variants when the container holds more than 2 panels: body padding 14px, panel padding 16px, inter-panel gap 16px, button padding 9px 18px
• Padding has a floor. Even when compacting, keep ~12px of padding inside a bordered or tinted panel (8px absolute minimum). Trim inter-panel gaps and font sizes before you starve the panel's own padding. Text or controls flush against a panel edge read as cramped and unfinished
• Never let content overflow: if overflow: hidden is set on the body, clipped controls are invisible and unusable
• Test mentally: count the vertical space budget (panels × padding + gaps + content height) and ensure it fits within a typical side-panel height (~400–500px)

Scrollable Panels (When Content Exceeds the Container)

When the control set genuinely can't be compacted further (4+ panels, mixed sliders + toggles + buttons), make the panel container scroll instead of clipping. Keep body non-scrolling so the background gradient stays anchored, and let the inner .app (or whatever you named the flex column) scroll:

html, body {
    overflow: hidden;   /* body never scrolls; background gradient stays put */
}
 
.app {
    height: 100%;
    overflow-y: auto;
    overflow-x: hidden;
    scrollbar-width: thin;                                    /* Firefox */
    scrollbar-color: rgba(255, 255, 255, 0.12) transparent;   /* Firefox */
}
 
/* Chromium (uihtml uses CEF/Chromium) */
.app::-webkit-scrollbar { width: 6px; }
.app::-webkit-scrollbar-track { background: transparent; }
.app::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.10);
    border-radius: 3px;
    transition: background var(--t-fast);
}
.app::-webkit-scrollbar-thumb:hover { background: var(--accent-glow); }

Adapt the colors to the chosen palette:

Keep the scrollbar 6px wide and the thumb under 20% alpha; anything heavier breaks the style. Don't show track borders or arrows.

Design Guardrails

These are cross-cutting rules that apply on top of whatever style is chosen. They exist to keep generated control panels from reading as "AI made that." A named built-in style that deliberately uses one of these moves as its identity (Cosmic Dark's neon glow, Midnight Gradient's blue-to-purple, Clean's glass) is intentional voice and is fine. The guardrails target the unconscious reflex of reaching for these on every panel.

Contrast (verify, don't eyeball)

• Body and label text must hit ≥4.5:1 against its background; large or bold text (≥18px, or ≥14px bold) needs ≥3:1. UI component boundaries, slider tracks, toggle outlines, and icons also need ≥3:1.
• Value readouts and placeholder text need the full 4.5:1 too: don't let a "tertiary" gray slip below it just because it's secondary information. The single most common failure is muted gray text on a tinted near-white (light styles) or a low-contrast gray on near-black (dark styles). If contrast is even close, push the text toward the ink end of the ramp.
• Gray text on a colored surface looks washed out. On an accent-colored button or panel, don't use neutral gray for the label: use white/near-white, a darker shade of the surface's own hue, or an alpha of the text color.

Numeric readouts

• Slider value displays, counters, and any aligned numbers get font-variant-numeric: tabular-nums so the width doesn't jitter as digits change while dragging.

Motion

• Reduced motion is not optional. Every non-trivial transition or entrance animation needs a @media (prefers-reduced-motion: reduce) fallback, typically a crossfade or an instant state change. Include this in the template's <style> block:

``css @media (prefers-reduced-motion: reduce) { *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; } } ``

• Reveal/entrance animations must enhance an already-visible default. Don't gate a control's visibility on a class-triggered transition. Inside uihtml (a headless Chromium/CEF render) a transition that never fires ships the panel blank.
• Timing. A control panel is a task UI: no page-load choreography; users are here to do something and won't wait for it. Durations: 100–150ms for instant feedback (press, toggle, value change), 200–300ms for state changes (menu open, panel expand). Keep interactive feedback under ~200ms so it feels instant. Run exit transitions at ~75% of their entrance duration.
• Easing. Ease out with an exponential curve; never bounce or elastic. Define one as a token and reuse it:

``css --ease-out-quart: cubic-bezier(0.25, 1, 0.5, 1); /* smooth */ --ease-out-quint: cubic-bezier(0.22, 1, 0.36, 1); /* snappier */ --ease-out-expo: cubic-bezier(0.16, 1, 0.3, 1); /* decisive */ ``

A subtle spring/compression on a control press is fine; a bouncy elastic entrance applied uniformly to every panel is a tell.

• Animate transform / opacity / filter, not layout properties (width, height, top, margin).

Structure & interaction

• Panels are this skill's "cards": never nest a panel inside a panel. Group related controls in one panel; separate groups with spacing or a hairline, not a second layer of container.
• Dropdowns and custom menus get clipped by the container. Because uihtml panels frequently set overflow: hidden or overflow: auto (see Scrollable Panels above), a position: absolute menu inside them is cut off. The reliable fix across uihtml's embedded Chromium is `position: fixed` with coordinates computed from the trigger's getBoundingClientRect() (flip above / left when near a viewport edge). Native <dialog> + showModal() (top layer) also escapes clipping. The Popover API and CSS anchor positioning are cleaner but need a recent Chromium. Only rely on them if you've confirmed the installed MATLAB's uihtml renderer supports them; otherwise fall back to position: fixed.
• Provide a visible :focus-visible state for keyboard users: ≥3:1 against adjacent colors, 2–3px, offset outside the element. A box-shadow ring or outline + outline-offset both work; never ship outline: none with no replacement.
• Build a small semantic z-index scale (e.g. dropdown → sticky → modal → tooltip) rather than arbitrary 999 / 9999.

Interactive states

Every control needs its states designed, not just the default. Keyboard users never see :hover, so focus is separate from hover and is not optional.

Loading / error / success are usually driven from the MATLAB backend; see matlab-uihtml-app-builder for the event wiring (e.g. SimComplete / SimError, busy-button state machine).

Refuse-and-rewrite (AI-slop tells)

If you're about to write any of these, restructure instead:

• Side-stripe accents: a thick colored bar down one edge of a panel, list row, callout, or alert. This is never the right answer; it reads instantly as "AI made that." It shows up in several disguises, and the ban covers all of them:

``css /* ❌ all of these render the same orange side-stripe */ .panel { border-left: 4px solid var(--accent); } /* the obvious one */ .panel { border-inline-start: 3px solid var(--accent); } /* logical-property alias */ .panel { box-shadow: inset 4px 0 0 var(--accent); } /* inset shadow, no border-left` in sight / .panel { border-width: 1px 1px 1px 4px; border-color: … var(--accent); } / asymmetric border widths */ .panel::before { content: ''; position: absolute; left: 0; width: 4px; height: 100%; background: var(--accent); }

/ ✅ mark state another way / .panel[data-state="active"] { border: 1px solid var(--accent); } / full hairline border / .panel[data-state="active"] { background: var(--accent-soft); } / an ~8% accent wash, defined as a token / .panel[data-state="active"] .title::before { content: '● '; color: var(--accent); } / leading glyph / ```

Rule of thumb: any left/right border wider than 1px, or any accent-colored fill narrower than ~8px running the full height of one edge, is a side-stripe. Rewrite it.

• Gradient text: background-clip: text over a gradient. Emphasize with weight, size, or a single solid color.
• Ghost-card: a 1px border and a soft wide box-shadow (blur ≥16px) on the same element. Pick one: a defined border, or a shadow at ≤8px blur.
• Over-rounding: border-radius ≥32px on panels or inputs. Panels top out around 12–16px; full-pill radius is only for tags and buttons.
• Cream/sand/beige body backgrounds by reflex and default purple-blue gradients or dark glows as generic decoration. If the chosen style doesn't call for them, don't add them.

Microcopy

Panel text is part of the design. Slop in a label or a status line reads as "AI made that" as loudly as a side-stripe does. These are engineer-facing MATLAB tools, so write like the product does: declarative, plain, and trusting the reader's competence.

• Labels & section headers are noun phrases, never questions or hype: "Initial Conditions", "Parameters", "Last Result", not "Ready to simulate?" or "Let's get started".
• Buttons are functional imperatives: "Run", "Reset", "Export PNG", "Stop". No exclamation points, no urgency, no emoji.
• Status, empty, and error messages state what happened, plainly: "Trajectory rendered (4449 pts)", "Nothing to export", "Invalid expression", not "Oops! Something went wrong 🎉" or "Success!".
• No slop words anywhere in UI text: leverage, unlock, seamless, powerful, streamline, supercharge, cutting-edge (and "robust" unless it means an actual engineering tolerance). No em dashes in microcopy: use a colon, comma, or period.
• Trust the engineer: don't gloss terms the audience already knows (σ, ρ, β, "attractor" need no explanation).

MATLAB-driven status text (wired in matlab-uihtml-app-builder) follows the same rules: the string that MATLAB sends to a status line is microcopy too.

Conventions

• Self-contained: No external CDN links; all CSS and JS inline in a single HTML file
• Responsive: Must work within arbitrary uihtml container sizes; use flexbox/grid with relative units
• MATLAB event boilerplate: Always include the setup(htmlComponent) function pattern:

function setup(htmlComponent) {
    window.htmlComponent = htmlComponent;
    // Listen for events from MATLAB
    htmlComponent.addEventListener("EventName", function(event) {
        // Handle event.Data
    });
    // Send events to MATLAB
    htmlComponent.sendEventToMATLAB("EventName", { key: value });
}

• Theme sync with MATLAB desktop: All templates listen for a SetTheme event. The MATLAB side can detect the desktop theme and push it to the HTML component. The `settings` path is R2025a+, so wrap it in try/catch with a sensible default so the app still works on older releases:

% Detect MATLAB desktop theme (R2025a+); fall back to a default on older releases
themeStr = 'dark';   % or 'light', whichever the style is designed for
try
    s = settings;
    themeStr = lower(char(s.matlab.appearance.MATLABTheme.ActiveValue));
catch
    % settings.matlab.appearance not available on this release; keep the default
end
 
sendEventToHTMLSource(htmlComp, "SetTheme", struct("theme", themeStr));

The HTML setup() function already includes a SetTheme listener that sets data-theme on the root element, triggering the CSS variable swap.

• Fonts: For a dense app UI a native system stack (-apple-system, 'Segoe UI', system-ui, sans-serif) is a legitimate, fast, offline-safe default. The built-in templates use one, and it's the right call for control panels. What reads as "AI made that" is reaching for a distinctive-but-overused display face for personality: Inter, Roboto, Geist, Space Grotesk, Plus Jakarta Sans, Fraunces (and plain Arial). Avoid those. If you pair fonts, pair on a real contrast axis (serif + sans); don't pair two similar sans-serifs. Also avoid purple-on-white cliches and cookie-cutter layouts; see the refuse-and-rewrite list in Design Guardrails above
• Accessible: Meet the contrast, focus-visible, interactive-states, and reduced-motion requirements in Design Guardrails above. Keep targets comfortably clickable (~28px+ hit area for toggles/thumbs, larger for buttons; size up toward 44px if the app may run on a touch display)
• Performance: CSS-only animations preferred; minimize JavaScript for visual effects
• External links: <a href="…" target="_blank" rel="noopener"> opens in the system default browser from uihtml, not inside the MATLAB figure. Useful for "view docs / view source" links in the app header. Style the link to fit the palette (accent color on hover, no underline by default):

``css .external-link { color: var(--text-secondary); text-decoration: none; transition: color var(--t-fast), text-shadow var(--t-fast); } .external-link:hover { color: var(--accent-secondary); text-shadow: 0 0 8px var(--accent-glow); /* dark styles */ } ``

Related Skills

• matlab-uihtml-app-builder: architecture, communication patterns, event handling, and MATLAB backend integration for uihtml apps. Use it for the functional wiring behind your styled controls.