Simple Flask-based file upload page

upload.py

import flask, werkzeug.utils, os, os.path

UPLOADS_DIR = "uploads"

if not os.path.exists (UPLOADS_DIR): os.mkdir (UPLOADS_DIR)

app = flask.Flask (__name__)

@app.route ("/")
def root ():
    return """
        <style>
            /* You know I had to do it to 'em */
            :root {
                --black: #000000;
                --green: #00FF00;
            }
            html {
                height: 100%;
                display: flex; align-items: center; justify-content: center;
            }
            body {
                height: 100%; margin: 0px;
                display: flex; flex-direction: column; align-items: center; justify-content: center;
            }
            body > * {
                margin: 10px;
            }
            html, body, input, button, p, small {
                background: var(--black);
            }
            button {
                border: 1px solid var(--green);
            }
            input, button, p, small {
                color: var(--green);
                font-family: monospace;
            }
        </style>
        <input type="file" name="file">
        <small>(Blame whoever wrote the spec for the file chooser not me)</small>
        <button>Submit</button>
        <p>Not started</p>
        <script>
            /* shitty code by eric reed 10-31-20. complaints go to 4403840834 */
            window.onerror = () => alert ("Shit went down, check console");
            var $ = selector => document.querySelector (selector);
            var ready = true;
            $ ("button").onclick = event => {
                if (!ready) return;
                if ($ ("input").files.length !== 1) return;
                var formData = new FormData ();
                formData.append ("file", $ ("input").files [0]);
                var xhr = new XMLHttpRequest ();
                xhr.upload.onprogress = event => {
                    $ ("p").innerText = `${event.loaded} / ${event.total} (${(event.loaded / event.total) * 100}%)`;
                };
                xhr.onreadystatechange = event => {
                    if (xhr.readyState == XMLHttpRequest.DONE) {
                        $ ("p").innerText = "Done";
                        ready = true;
                    }
                };
                xhr.open ("POST", "/upload", true);
                xhr.send (formData);
                ready = false;
            };
        </script>
    """

@app.route ("/upload", methods = ["POST"])
def upload ():
    _file = flask.request.files ["file"]
    _file.save (UPLOADS_DIR + os.path.sep + werkzeug.utils.secure_filename (_file.filename))
    return flask.redirect ("/")

if __name__ == "__main__":
    app.run ("0.0.0.0", 42069, ssl_context = ("cert.pem", "key.pem"))