black borders css code example
Example 1: white border css
border: solid white 4px;
Example 2: corner border css
<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta charset="utf-8">
<title></title>
<style>
#content {
width: max-content;
height: fit-content;
background:
linear-gradient(to right, black 4px, transparent 4px) 0 0,
linear-gradient(to right, black 4px, transparent 4px) 0 100%,
linear-gradient(to left, black 4px, transparent 4px) 100% 0,
linear-gradient(to left, black 4px, transparent 4px) 100% 100%,
linear-gradient(to bottom, black 4px, transparent 4px) 0 0,
linear-gradient(to bottom, black 4px, transparent 4px) 100% 0,
linear-gradient(to top, black 4px, transparent 4px) 0 100%,
linear-gradient(to top, black 4px, transparent 4px) 100% 100%;
background-repeat: no-repeat;
background-size: 20px 20px;
}
</style>
</head>
<body>
<div id="content"> </div>
</body>
</html>