当php中没有内容时更改背景颜色

I am working on a php/wordpress website in which I want to hide the background-color when there is no content.

The php code which I am using is:

<div class="featured-block__content">
    <h1 class="featured-block__tag"><?php echo esc_html( explode('|',get_the_title())[1]); ?></h1>
</div>

The css code for the above html/php code is:

.featured-block__content {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 85px;
    background-color: rgb(255, 255, 255);
    opacity: 0.831;
    z-index: 3;
    position: relative;
    bottom: 85px;
}

Problem Statement:

I am wondering what changes I need to make in the php code above so that where there is no content inside h1 tag, the background-color should be background-color: rgba(0, 0, 0, 0);

At this moment where there is content inside h1 tag, the background-color is background-color: rgb(255, 255, 255);

You can use the following:

<?php
    $h1_content = esc_html(explode('|', get_the_title())[1]);
?>

<div class="featured-block__content <?= trim($h1_content) === '' ? 'no-h1' : ''; ?>">
    <h1 class="featured-block__tag"><?= $h1_content; ?></h1>
</div>

With the following additional CSS:

.featured-block__content.no-h1 {
    background-color: rgba(0, 0, 0, 0);
}

In order to have PHP control the CSS, you'll need to output a new rule to DOM that the CSS can target.

In this case, you can add a class to the <h1>, by simply echoing out the desired class name when there's no content. esc_html() returns an empty string, so you can do a check against "".

The following adds a class black when this content is absent:

<h1 class="featured-block__tag" <?php if (esc_html(explode('|',get_the_title())[1]) === "") { echo "black"; } ?>>
  <?php echo esc_html(explode('|',get_the_title())[1]); ?>
</h1>

From here you can craft CSS that applies the desired rule to the new selector:

.black {
  background-color: rgb(0, 0, 0);
}

You can try

<h1 class="<?php esc_html( explode('|',get_the_title())[1]) === '' ? 'featured-block__tag bg-class1' : 'featured-block__tag'?>"><?php echo esc_html( explode('|',get_the_title())[1]); ?></h1>

and css

.bg-class1{
background-color: #yourcolor
}