how to present the categories in css code example

Example 1: css class

.myclass {
  border:1px solid black;
  background-color: #d2d2d2;
  height:20px;
  width:60px;
}
/*If you give this class to a div in html, it will get the styles you gave
to that class. You can add multiple classes to a div, and multiple divs
can get that class. */
/* I hope I helped! */

Example 2: syntax for manipulating a class in css

//element
element {
}
//class
.class {
}
//ID
#id {
}
//element and class
element .class {
}
//element with class and decendent
element.class decendent {
}