问用两种颜色的单行加下划线的文本

EN

h1 {
  display: inline-flex;
  flex-direction: column;
}
h1:after, 
h1:before {
  content: '';
  border-bottom: 1px solid green;
  order: 2;
  width: 50%;
}
h1:after {
  margin-left: auto;
  margin-top: -1px;
  border-color: red;
}

<h1>Lorem ipsum dolor sit.</h1>

h1 {
  max-width: 400px;
}
h1 span:first-child {
  text-decoration: red underline;
}
h1 span:last-child {
  text-decoration: green underline;
}

<h1><span>Lorem ipsum dolor </span><span>sit amet, consectetur.</span></h1>

class Title {
  constructor(text, parts = []) {
    this.text = text;
    this.parts = parts;
    return this.create()
  }

  checkLength() {
    let l = this.parts.reduce((r, e) => r + e.width, 0);
    if (l > 100) {
      throw new Error('Sum of all parts width must be under 100%')
    }
  }

  create() {
    this.checkLength();
    let title = this.createTitle();
    this.addLines(title);
    return title;
  }

  createTitle() {
    let h1 = document.createElement('h1');
    h1.textContent = this.text;
    h1.style.display = 'inline-block';
    h1.style.position = 'relative';
    return h1;
  }

  createLine(input) {
    let {color,width} = input;
    let line = document.createElement('span');
    line.style.position = 'absolute';
    line.style.bottom = 0;
    line.style.border = '1px solid ' + color;
    line.style.width = width + '%';
    return line;
  }

  addLines(title) {
    let that = this;
    this.parts.forEach(function(part) {
      let line = that.createLine(part);
      line.style.left = this.prev + '%';
      this.prev += part.width;
      title.appendChild(line)
    }, {prev: 0})
  }
}


let title = new Title('Random Title', [
  {color: 'red', width: 60},
  {color: 'blue', width: 20},
  {color: 'green', width: 20}
])

let title2 = new Title('Lorem ipsum dolor.', [
  {color: 'black', width: 80},
  {color: 'green', width: 20}
])


document.body.appendChild(title)
document.body.innerHTML += '<br>'
document.body.appendChild(title2)