anchor(<a>...</a>) in the section before another section cannot be clicked when using layout

[mikelue]

Problem

1. The <a>..</a> cannot be clicked when using layout.
2. Even for the section, it cannot be drag-and-select.

My Environment

1. Java 8
2. Maven 3.3.3
3. maven-site-plugin 3.4.1-SNAPSHOT

Example

sandbox.md

1. The link in "Chapter 1" cannot be clicked
2. The link in "Chapter 2" is fine

## Chapter 1

[Google](https://www.google.com)

---

## Chapter 2

[Google](https://www.google.com)

site.xml

<project
    xmlns="http://maven.apache.org/DECORATION/1.6.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/DECORATION/1.6.0 http://maven.apache.org/xsd/decoration-1.6.0.xsd"
>

<custom>
    <reflowSkin>
        <pages>
            <sandbox>
                <sections>
                    <columns>2</columns>
                    <columns>2</columns>
                </sections>
            </sandbox>
        </pages>
    </reflowSkin>
</custom>

</project>

Diagnosis

In the file reflow-skin.css, if I remove the content:""; property:

h1[id]:before,
h2[id]:before,
h3[id]:before,
h4[id]:before,
h5[id]:before,
h6[id]:before,
a[name]:before {
    display:block; 
    /* content:""; */
    height:90px; 
    margin:-90px 0 0; 
}

The problem would be solved.
But I have no idea if this is a sensible solution.