php页面中怎么设置字间距

<style>
    p {
        letter-spacing: 2px;
    }
</style>

<p>Hello World!</p>

<?php
// 创建一个300x100的图片
$image = imagecreatetruecolor(300, 100);

// 定义颜色
$black = imagecolorallocate($image, 0, 0, 0);
$white = imagecolorallocate($image, 255, 255, 255);

// 定义字体
$font = 'arial.ttf';

// 定义字体大小
$font_size = 36;

// 写入字符串
$text = 'Hello World!';
$text_box = imagettfbbox($font_size, 0, $font, $text);

// 计算字符串所占据的宽度和高度
$text_width = $text_box[2] - $text_box[0];
$text_height = $text_box[1] - $text_box[7];

// 计算宽度和高度偏移量
$x_offset = (300 - $text_width) / 2;
$y_offset = (100 - $text_height) / 2;

// 写入字符串
imagettftext($image, $font_size, 0, $x_offset, $y_offset, $black, $font, $text);

// 输出图片
header('Content-Type: image/png');
imagepng($image);

// 释放内存
imagedestroy($image);
?>

<?php
require_once('tcpdf/tcpdf.php');

$pdf = new TCPDF();
$pdf->AddPage();
$pdf->SetFont('helvetica', '', 14);
$pdf->Cell(0, 0, 'Hello World!', 0, 1, 'C', 0, '', 0, false, 'T', 'M');
$pdf->Output();
?>