Replacing substrings of nested arrays with a value from another array

The loop below outputs from the $defaultValues values, there are 2 nested arrays in this array which are “colors” and “lessons”.

This loop also takes the substring values from the $search array and replaces them with the values from the $replace.

Question: How to replace nested array clause value “colors” and “lessons” from $defaultValues

values: “colors”=>[“4”, “5”, “6”] and “lessons” =>[“7 ” , ” 8″, “9”] from $replace”

I can’t figure out how to do this, my current code outputs this:

Name: 1
Age: 2
Whe are u from: 3
Your favorite color: 4
Choose courses: 7
Your comment: 10

I would like the code to output this:

Name: 1
Age: 2
Whe are u from: 3
Your favorite color: 4,5,6
Choose courses: 7,8,9
Your comment: 10

$defaultValues = [
"name"     =>  "Name:                   <div class='user'>     write your name                     </div>", 
"age"      =>  "Age:                    <div class='age'>      enter your age                      </div>",
"from"     =>  "Whe are u from:         <div class='from'>     write where are you from            </div>", 
"colors"   =>  ["Your favorite color:   <div class='colors'>   you didn't say your favorite color  </div>"],        
"lessons"  =>  ["Choose courses:        <div class='lessons'>  you have not chosen any course      </div>"],
"comment"  =>  "Your comment:           <div class='comment'>  no comments                         </div>",     
];
 
$search = [
"name"     =>  "write your name", 
"age"      =>  "enter your age", 
"from"     =>  "write where are you from", 
"colors"   =>  ["you didn't say your favorite color"],        
"lessons"  =>  ["you have not chosen any course"],
"comment"  =>  "no comments",   
];
 
$replace = [
"name"     =>  "1", 
"age"      =>  "2",
"from"     =>  "3",
"colors"   =>  ["4", "5", "6"],        
"lessons"  =>  ["7", "8", "9"],
"comment"  =>  "10",       
];
 
 
foreach($defaultValues as $key => $items){
echo "<div class='block'>";
 
if(is_array($items)){
foreach($items as $child){
$items = str_replace($search[$key], $replace[$key], $child);
}}
 
echo $items = str_replace($search[$key], $replace[$key], $items);   
 
echo "</div>";  
}