_getCSSLeft(x) {
    if (x === undefined || x === null) {
      return {
        left: 0
      };
    }

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