What is the problem with these class selector

Tell us what’s happening:
Describe your issue in detail here.

  **Your code so far**
/* file: index.html */
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Colored Markers</title>
  <link rel="stylesheet" href="styles.css">
</head>
<body>
  <h1>CSS Color Markers</h1>
  <div class="container">
    <div class="marker one">
    </div>
    <div class="marker">
    </div>
    <div class="marker">
    </div>
  </div>
</body>
</html>
/* file: styles.css */
h1 {
text-align: center;
}

.marker {
width: 200px;
height: 25px;
margin: 10px auto;
}

.marker one{
background-color:red;
}

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36

Challenge: Step 18

Link to the challenge:

.mark one = Target the element one inside the element with class .mark

We can use multiple class names inside an element and we can target that element with all the class names or just one.

for example:

<span class="class1 class2"></span>

.class1.class2 = we target all elements that have both class1 and class2, we don’t use space between class names

.class1 .class2 = we target the element that have .class2 and must be inside an element that have class1, we use space between class names

.class2 = we target all elements that have class2