Computed style

Let's say we want to find all anchor links that are red. They could be red because of the inline style, or some CSS class. We need to filter all anchor links by the computed style. Let's use a combination of cy.get and cy.filter commands.

<a href="article1.html" class="help external">Article 1</a>
<a href="article2.html" class="help">Article 2</a>
<a href="article3.html" class="help external">Article 3</a>
<a href="index.html" class="help" style="color: red"
  >Full Index</a
>
<style>
  .external {
    color: red;
  }
</style>

cy.get('a')
  // using the jQuery filter function
  // https://api.jquery.com/filter/
  // to filter all elements yielded by the parent command
  .filter((k, el) => {
    const color = window.getComputedStyle(el).color
    // the computed color is an RGB string
    // with each channel going from 0 to 255
    return color === 'rgb(255, 0, 0)'
  })
  // 3 anchor links are red
  .should('have.length', 3)

Tip: instead of using camel-case property name, you can call the getPropertyValue method on the object returned by the window.getComputedStyle method:

cy.get('selector')
  .then(($el) => {
    return window.getComputedStyle(el)
  })
  .invoke('getPropertyValue', 'text-decoration')
// yields the string

Watch the video Select Elements By Computed Style.