_getCSSRight(x) {
    if (x === undefined || x === null) {
      return {
        right: 0
      };
    }

    const {innerWidth, marginRight} = this.props;
    return {
      right: marginRight + innerWidth - x
    };
  }
Get the right coordinate of the hint.
When x undefined or null, edge case, pin right.
@param {number} x X.
@returns {{right: *}} Mixin.
@private