Allow Sass statements in @font-face and keyframe-step bodies #11825

Description

SCSS permits statements such as @include and @if inside @font-face blocks and keyframe steps. These hosts use declaration-oriented CSS body rules, so statement children can be rejected or interfere with following descriptors and declarations.

@mixin font-options {
  font-display: swap;
}

@font-face {
  @include font-options;
  @if true { font-weight: 400; }
  font-family: Example;
  src: url(example.woff2);
}