I did it what is the problem

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

where will it be used?
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" type="text/css" href="styles.css">
</head>
<body>
  <h1>CSS Color Markers</h1>
  <div class="container">
    <div class="marker red">
      <div class="cap"></div>
      <div class="sleeve"></div>
    </div>
    <div class="marker green">
    </div>
    <div class="marker blue">
    </div>
  </div>
</body>
</html>
/* file: styles.css */
h1 {
text-align: center;
}

.container {
background-color: rgb(255, 255, 255);
padding: 10px 0;
}

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

.cap {
width: 60px;
height: 25px;

}

.sleeve {
width: 110px;
height: 25px;
background-color: rgba(255, 255, 255, 0.5);

}

.cap .sleeve {
display: inline-block;
}

.red {
background: linear-gradient(rgb(122, 74, 14), rgb(245, 62, 113), rgb(162, 27, 27));
}

.green {
background: linear-gradient(#55680D, #71F53E, #116C31);
}

.blue {
background: linear-gradient(hsl(186, 76%, 16%), hsl(223, 90%, 60%), hsl(240, 56%, 42%));
}

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36

Challenge: Step 78

Link to the challenge:

you should add comma after every class

.cap, .sleeve {
      ...
}

why doesn’t it work when ı insert the codes their sections separately. ı mean like below:
.cap {
display: inline-block;
}
.sleeve {display: inline-block;
}

the course wants you to know that you can target multiple classes in the same bracket if they have the same code

ı see thanks a lot have a nice coding day