Instead of
return {
statusCode: 200,
body: 'Test',
}
Use
return {
statusCode: 200,
headers: {
'Content-type': 'text/html; charset=UTF-8',
},
body: '<body style="background-color: black;"><h2 style="color: white; padding-top:200px; text-align: center; font-family: system-ui">Test</h2></body>',
}