Data-Dense Dashboard Designer

6. The traps that only appear when you measure

Every one of these was found on a screen that looked finished. The first group a gate caught; the ones marked "no gate sees it" were caught by opening the screenshot and looking, which is why that step is not optional:

• A chart palette is not a text palette. White initials on --color-chart-4 measured 2.65:1 in dark. Chart colours are tuned for large filled shapes.
• Success green as text on a raised surface measured 4.43:1 - four hundredths short of AA. Put the colour on the icon and the sign; keep the text neutral.
• axe must not run mid-transition. Disable transitions before flipping the theme, or contrast is sampled while colours are still moving.
• Dense tables do not fit a phone. Drop the column a phone can lose - the sparkline, the derived value - in a media query, and say so in a comment. Do not shrink type below the scale.
• Stagger comes from a token: calc(var(--duration-fast) * 0.6 * n), never a typed millisecond.
• A grid row stretches its items. Two fields side by side where only one has a hint: the hint-less control grows to match the taller column and the two inputs end up different heights. Set align-content: start on the field and an explicit block-size on the control. Measure the heights in the render - the difference is obvious in a screenshot and invisible in the markup.
• The same stretch hits whole panels, and no gate sees it. A row is as tall as its tallest panel, and the short one packs its content to the top and ends in a bordered void - a heatmap panel with 130px of nothing under the caption, a right column that stops two panels short of the map beside it. Every panel in a row has to say which it is: one child absorbs the slack (grid-template-rows:auto minmax(0,1fr), and that child's own tracks go minmax(<min>,1fr) so its rows grow too), or the rows share it out (align-content:space-between), or the short column earns another panel. Screenshot the row and look at the bottom edge of each panel; this never shows up in the markup.
• auto-fit silently drops a column, and no gate sees it. Three gauges in a panel about 340px wide with minmax(min(100%,7rem),1fr) resolved to two tracks and orphaned the third beside an empty cell. When the count is fixed and meaningful, write repeat(3,minmax(0,1fr)) and give narrow widths their own rule.
• A category chart needs its categories on the page, and no gate sees it. A Pareto of five defect types whose names live only in the aria-label is a row of anonymous bars to everyone looking at it. Put the labels under the bars - lay the plot out on an even pitch inside its viewBox so a matching grid of labels lines up without a second coordinate system.
• An .sr-only needs a positioned ancestor. Inside a scroller it otherwise resolves against the initial containing block, lands outside the viewport, and inflates the document's scroll width by hundreds of pixels.
• A zero-area element that only has area while it animates reads as content lost under prefers-reduced-motion. Give a radar sweep a wedge, not a 1px line.
• Never reuse a class name across layout and colour. .c4 as both a four-column span and the fourth chart colour painted an entire panel pink.

7. The loop

node ${CLAUDE_SKILL_DIR}/../../../scripts/measure_render.mjs <file> && node ${CLAUDE_SKILL_DIR}/../../../scripts/measure_render.mjs --dark <file>
node ${CLAUDE_SKILL_DIR}/../../../scripts/verify_states.mjs <file>  && node ${CLAUDE_SKILL_DIR}/../../../scripts/axe_audit.mjs --dark <file>
node ${CLAUDE_SKILL_DIR}/../../../scripts/verify_responsive.mjs <file> --scale=1.25
node ${CLAUDE_SKILL_DIR}/../../../scripts/verify_interactive.mjs <file>
node ${CLAUDE_SKILL_DIR}/../../../scripts/slop_tells.mjs --strict <file> && node ${CLAUDE_SKILL_DIR}/../../../scripts/taste_audit.mjs --strict <file>

Then screenshot it and look, in both themes, at 1600 and 390 wide. The gates will pass a chart that is drawn wrong. A correlation matrix that is not symmetric is 16/16 green and still embarrassing.

Worked references, both gate-verified: ${CLAUDE_SKILL_DIR}/../../../examples/showcase/index.html (revenue console) and ${CLAUDE_SKILL_DIR}/../../../examples/terminal/index.html (trading desk, ten chart types).