面积样条线:边到边线并隐藏第一个y标签

我收到了一个使用areaspline的图形模型(忽略柱状图):

1. 有没有一种方法可以根据它们的趋势斜率,或者可能只是稍微高于或低于端点,将这些线延伸到图形的边缘?在这样的图上,省略这些边线看起来不错,但在同一区域中只有3个数据点的图上,空白更为明显。
2. 我让y轴标签彼此步进,但在这种情况下,我似乎找不到隐藏第一个标签(0美元)的方法。除了隐藏文本元素本身之外,还有这样的配置吗?

编辑

var themeColors = {
    primaryColor: '#067bc2',    //dark blue
    secondaryColor: '#6a61a7',  //dark purple
    tertiaryColor: '#5ccadc',   //turquoise
    darkGray: '#37383e',        //dark gray
    mediumGray: '#919aa2',      //medium gray
    mediumLightGray: '#c9d3dc', //medium blue gray
    lightGray: '#eaf1f8',       //light blue gray (hover color)
    primaryRed: '#e54443',
    secondaryRed: '#e54443',
    primaryGreen: '#2bbb2d',
    secondaryGreen: '#2bbb2d',
    primaryOrange: '#ffa883',   //peach
    primaryBackground: '#fafcfe',//light blue
    secondaryBackground: '#ffffff',
    primaryText: '#37383e',     //dark gray
    secondaryText: '#919aa2',   //medium gray
    selectedColor: '#f5fafd'    //light blue, slightly darker than background
};

var colors = [
  themeColors.secondaryColor,
  themeColors.tertiaryColor,
  themeColors.primaryOrange
];

(function renderChart(series) {
  var options = {
    chart: {
      height: 400,
      spacing: [0,0,0,0],
      type: 'areaspline',
    },
    colors: colors,
    credits: { enabled: false },
    legend: {
      align: 'left',
      itemStyle: {
        color: themeColors.secondaryText,
        fontSize: '12px',
        fontWeight: 'normal',
      },
      margin: 30,
      symbolHeight: 14,
      symbolRadius: 0,
      symbolWidth: 14,
    },
    plotOptions: {
      areaspline: {
        marker: {
          fillColor: themeColors.secondaryBackground,
          lineColor: null,
          lineWidth: 2,
          radius: 3,
          symbol: 'circle',
        }
      }
    },
    title: { text: null },
    xAxis: {
      categories: ['first', 'second', 'third'],
      crosshair: {
        color: Highcharts.color(themeColors.lightGray).setOpacity(.5).get('rgba'),
        width: 12
      },
      labels: {
        style: {
          color: themeColors.secondaryText,
          fontSize: '12px'
        }
      },
      lineColor: themeColors.lightGray,
      tickColor: themeColors.lightGray,
      tickWidth: 0,
    },
    yAxis: {
      gridLineColor: themeColors.lightGray,
      labels: {
        align: 'left',
        step: 2,
        style: {
          color: themeColors.secondaryText,
          fontSize: '12px'
        },
        x: 0,
        y: 12,
      },
      lineColor: themeColors.lightGray,
      tickColor: themeColors.lightGray,
      title: { text: null },
    },
  };

  series.forEach((s,i)=>{
    s.fillColor = {
      linearGradient: {
        x1: 0,
        y1: 0,
        x2: 0,
        y2: 1
      },
      stops: [
        [0, Highcharts.color(colors[i]).setOpacity(0.1).get('rgba')],
        [1, Highcharts.color(colors[i]).setOpacity(0).get('rgba')]
      ]
    };
  });

  options.series = series;

    Highcharts.chart('container',options);
})([
    { name: 'a', data:[1,4,2] },
  { name: 'b', data:[3,1,2] }
]);

JSFIDLE: https://jsfiddle.net/mtowj6ng/

谢谢