code: function getKeyframesBlocks() {
    const type = NodeType.BlockType;
    const token = tokens[pos];
    const line = token.ln;
    const column = token.col;
    const keyframesBlocksEnd = token.block_end;
    let content = [];
  
    while (pos < keyframesBlocksEnd) {
      if (checkSC(pos)) content = content.concat(getSC());
      else if (checkKeyframesBlock(pos)) content.push(getKeyframesBlock());
      else if (checkAtrule(pos)) content.push(getAtrule()); // @content
      else break;
    }
  
    return newNode(type, content, line, column);
  }
docs: Get all keyframe blocks - `5% {} 100% {}`
  @return {Node}