// your variant
function render() {
    $str = "<div style = \"background-color:RGB(".$this->color->red.','. $this->color->green .','. $this->color->blue.");width:".$this->width."px;height:".$this->height.'px;';
    $str .= "margin: " . $this->top. 'px '. $this->left.'px;';
    $str .= "\"></div>";
    echo $str;
}


// my variant
function render() {
    $str = "<div style = \"background-color:RGB( {$this->color->red}, {$this->color->green}, {$this->color->blue} ); width:{$this->width}px; height:{$this->height}px;";
    $str .= "margin: {$this->top}px {$this->left}px;";
    $str .= '"></div>';
    echo $str;
}