Use SCSS instead of inline Styles

[maxigimenez]

At the moment we need to use inline CSS due to the shadow-dom and the encapsulation:

getStyles(): HTMLStyleElement {
    const stylesheet = document.createElement('style');
    stylesheet.innerHTML = `
      .my-component {
        border: 1px solid red;
      }
    `;
    return stylesheet;
  }

It would be nice to remove this implementation in favor of write SASS or CSS and import the generated styles into the web-component.