title: How to add gradient color in echarts?
body: <p>I made a echart <a href="https://stackblitz.com/edit/angular-aqghec?file=src%2Fapp%2Fapp.component.ts" rel="nofollow noreferrer">line graph</a>.
  Now, I want to add gradient color to it, as shown below:
  <a href="https://i.stack.imgur.com/SStjz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SStjz.png" alt="enter image description here" /></a></p>
  <p>In this <a href="https://echarts.apache.org/en/option.html#series-line.areaStyle.color" rel="nofollow noreferrer">link</a>, it said it supports the setting as gradient color. But when I tried to do this as code given:<a href="https://i.stack.imgur.com/fIqiN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fIqiN.png" alt="enter image description here" /></a></p>
  <p>It gave this error:
  <a href="https://i.stack.imgur.com/zSgRu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zSgRu.png" alt="enter image description here" /></a></p>
  <p>What to do?</p>
  <p>Thanks in advance.</p>