how to make a square in html code example

Example 1: how to create a shape in css

div {
	clip-path: polygon(100% 100%, 100% 100%, 100% 100%)
}

Example 2: how to make a square line in html

<div style="width:500px;height:100px;border:1px solid #000;">This is a rectangle!</div>

Example 3: tina4 shape html

echo _doctype()._html(
        _head(_title("Hello World!")),
        _body(
        _div(
        _h1("Hello World!",
            _b("Another tag",
                _p("Testing")
            )
        ),
        _p(["style" => "border: 1px solid red"], "This should have a red border")
        )));