details-and-accessibility.md

Details and accessibility

Underlines, selection, forms, decorative text and the floors that keep everything readable.

Underlines

Default underline position is browser-determined, sometimes too close, sometimes cutting through descenders, sometimes too thin. Pull position and thickness from the font's own metrics:

a {
  text-underline-position: from-font;
  text-decoration-thickness: from-font;
}

A dotted underline on an abbreviation:

abbr {
  text-decoration: underline dotted;
}

Or tune manually:

a {
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  text-decoration-skip-ink: auto;
  text-decoration-color: var(--color-gray-1000);
  transition: text-decoration-color 200ms ease-out;
}

a:hover {
  text-decoration-color: var(--color-gray-1200);
}

Animate the custom element however the effect requires.

Selection

::target-text styles the phrase a shared link scrolls to.
The Custom Highlight API styles ranges you pick yourself, like search matches, without extra markup.

Forms and editable text

::placeholder styles the hint in an empty field.
caret-color colors the blinking insertion bar. Color is about as far as caret styling goes; a fully custom caret is hard to build and rarely worth it.

iOS input zoom

This is an accessibility feature: 16px is the web default, and Safari treats smaller as too hard to read while typing.

The two fixes differ in what they do to the design, not in correctness.

Size up on mobile. The input renders at 16px on small screens and drops to the design size from the sm breakpoint up. Nothing to compensate, but the mobile input no longer matches the desktop one.

<input className="text-base sm:text-sm" type="email" />

Scale the text down. Keep font-size at 16px so Safari never zooms, then render at the intended size with a transform. The design survives at every viewport, at the cost of two compensating calcs. Widen the element by the inverse of the scale so it still fills its container once shrunk, and divide line-height by the same factor so the intended leading survives. origin-left pins the text to the start edge, origin-right under RTL. Above the breakpoint, drop the transform and set the real size.

// 13px rendered from a 16px font-size: 13 / 16 = 0.8125
<div className="flex h-10 items-center rounded-[10px] bg-gray-300 px-2.5">
  <input
    className="h-full w-[calc(100%/0.8125)] origin-left scale-[0.8125] bg-transparent text-base leading-[calc(1.125/0.8125)] outline-none sm:w-full sm:scale-100 sm:text-[13px]"
    type="email"
  />
</div>

The transform shrinks the whole box, not only the glyphs, so let a wrapper draw the field's surface and keep the input transparent. A background, border, or ring on the scaled element shrinks with the text and misses the intended hit area.

Decorative text

Property	Effect
`::first-letter`	Drop cap, widely supported
`::first-line`	Styles only the first line
`initial-letter`	Sizes the drop cap; limited support, no Firefox yet
`background-clip: text`	Clips a background or gradient to the letter shapes
`-webkit-text-stroke`	Outlines the letters; works across modern browsers despite the prefix
`text-shadow`	Like `box-shadow` but follows the character shapes

A text stroke drawing lines inside the letters is the font. The stroke traces every contour, and variable fonts usually keep overlapping shapes unmerged. Static fonts do not have this issue.

Sizes

Typography must survive the reader changing it: zoom, a larger browser font size, an overridden line height or letter spacing.

Text	Size
Long-form body starting point	Around `16px`, verified in the actual typeface and measure
Inputs and menus starting point	Around `14px`
Captions	`13px`
Floor	Rarely below `12px`

Font smoothing

Tailwind's antialiased sets both properties:

html {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

<html lang="en">
  <body class="font-sans antialiased">
    <main>{children}</main>
  </body>
</html>

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