Why aren't my self-signed certificates working for HTTPS on localhost

Question

I have this in Node.js:

const http2 = require('http2')
const fs = require('fs')
let server
start({
  port: process.env.PORT || 3000,
  private: fs.readFileSync('/Users/me/certs/localhost.key').toString(),
  public: fs.readFileSync('/Users/me/certs/localhost.crt').toString()
})
async function start(opts) {
  server = await createServer(opts)
}
async function createServer({ port, private, public, password }) {
  return new Promise((res, rej) => {
    let server = http2.createSecureServer({
      key: private,
      cert: public,
      passphrase: password,
      allowHTTP1: true,
      secureProtocol: 'TLSv1_2_method'
    }, handleServerRequest)
server.listen(port, fault => {
  if (fault) {
    rej(fault)
  } else {
    res()
  }
})

})
}
async function handleServerRequest(req, res) {
  console.log('here')
}

I generated my certs (and I think added it to the trust store on my computer) like this:

mkdir ~/certs
cd ~/certs
openssl req -x509 -sha256 -nodes \
  -subj '/CN=localhost' \
  -newkey rsa:2048 -days 365 \
  -keyout localhost.key -out localhost.crt
open localhost.crt # add it to something? login?
sudo security add-trusted-cert \
  -p ssl -d -r trustRoot \
  -k ~/Library/Keychains/login.keychain localhost.crt

However, upon running the Node.js server and visiting https://localhost:3000, I get this:

What am I doing wrong? How do I fix it?