A selector list is a comma-separated list of selectors that share the same style rule.
A selector list consists of multiple selectors separated by commas:
selector1, selector2 {...}
The following two USS snippets have the same effect.
# container2 {
  background-color: pink;
  border-radius: 10px;
}
Button {
  background-color: pink;
  border-radius: 10px;
}
# container2, Button {
   background-color: pink;
     border-radius: 10px;
 }