`font-display` CSS at-rule descriptor

The font-display descriptor for the @font-face at-rule determines how a font face is displayed based on whether and when it is downloaded and ready to use.

Syntax

css

/* Keyword values */
font-display: auto;
font-display: block;
font-display: swap;
font-display: fallback;
font-display: optional;

Values

auto: The font display strategy is defined by the user agent.
block: Gives the font face a short block period and an infinite swap period.
swap: Gives the font face an extremely small block period and an infinite swap period.
fallback: Gives the font face an extremely small block period and a short swap period.
optional: Gives the font face an extremely small block period and no swap period.

Note: In Firefox, the preferences gfx.downloadable_fonts.fallback_delay and gfx.downloadable_fonts.fallback_delay_short provide the duration of the "short" and "extremely small" periods, respectively.

Description

The font display timeline is based on a timer that begins the moment the user agent attempts to use a given downloaded font face. The timeline is divided into the three periods below which dictate the rendering behavior of any elements using the font face:

Font block period: If the font face is not loaded, any element attempting to use it must render an invisible fallback font face. If the font face successfully loads during this period, it is used normally.
Font swap period: If the font face is not loaded, any element attempting to use it must render a fallback font face. If the font face successfully loads during this period, it is used normally.
Font failure period: If the font face is not loaded, the user agent treats it as a failed load causing normal font fallback.

Formal definition

Related at-rule	`@font-face`
Initial value	`auto`
Computed value	as specified

Formal syntax

font-display = 
  auto      |
  block     |
  swap      |
  fallback  |
  optional

Examples

undefined

Specifying fallback font-display

css

@font-face {
  font-family: "ExampleFont";
  src:
    url("/path/to/fonts/example-font.woff") format("woff"),
    url("/path/to/fonts/example-font.eot") format("embedded-opentype");
  font-weight: normal;
  font-style: normal;
  font-display: fallback;
}

Specifications

CSS Fonts Module Level 4

font-display CSS at-rule descriptor