The <base> tag specifies the default address or default destination for all links on the page.
Normally, the browser will extract the corresponding element from the URL of the current document to fill in the blanks in the relative URL.
Use the <base> tag to change this. The browser will then no longer use the URL of the current document, but use the specified base URL to parse all relative URLs. This includes URLs in the <a>, <img>, <link>, <form> tags.
test:
1: The link path placed in front of the base tag can use the relative path and is relative to the current path.
But the link placed behind it uses the relative path that will be relative to the path specified by the base.
2: After using the base tag, the relative path of the link in the body will be relative to the path specified by the base.
3: After using the default base target, the subsequent opening method will be opened in the manner specified by base, unless the opening method is defined later.
Summary: base is actually to define a default address and default target. All link elements after it will work.