Property Reference - CSS Reference - page 300

Name
rest-before
Values:
none | x-weak | weak | medium | strong | x-strong | <time>
Initial value:
User agent-dependent
Applies to:
All elements
Inherited:
No
Computed value:
Not specified, but likely an absolute time value
Description:
Defines the length of a rest that precedes the audio rendering of an element's content. A rest is
an interval in which no content is audibly rendered, although background sounds may still be
audible. The rest is rendered before the element's content but after any cue that precedes the
element (see cue-before and related properties).
Examples:
th {rest-before: 0.5s;}
strong {rest-before: 333ms;}