Php: how to add style input element through class

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PHP

I have a class Form, which has` write(), attr($key,$value) and addClass($array) methods. The write() method print an input element` type="$this->type", the attr($key,$value) method gives attribute to that input element, and the addClass($array) method gives style to that input element. I have written the write() and attr($key,$value) methods, everything is normal, it's work, but i have some problems with addClass($array) method.
For example`

$f = new TextElement();
$f->attr("value","#97BEF0");
$f->addStyle(array("color"=>"red", "font-size"=>"20px"));
$f->write();

Btw, i also have a class TextElement, which is inherited from class Form.

What I have tried:

class Form{
	public $type;
	public $attr = "";
	public $arr = array();
       //print input
	function write(){
		print "<input type='$this->type' $this->attr style='$this->arr'>";
	}
        //add attribute
	function attr($key,$value){
		$this->attr .= "$key='$value'";
	}
        //add style
	function addStyle($array){
		for($i = 0; $i < count($array); $i++){
			$this->arr = $array[$i];
		}
	}
}

class TextElement extends Form{
	function __construct(){
		$this->type = "text";
	}
}

$p = new TextElement();
$p->attr("value","#97BEF0");
$p->addStyle(array("color"=>"red", "font-size"=>"20px"));
$p->write();

So my problem is with addStyle($array) method, How must i give parameters to an array? It gives me error` Nitice: Array to string conversion.