Set the height on the submit button in ‘em’. When you increase the text size the ‘Submit’ text gets cut-off.
The placeholder text shouldn’t just basically repeat the label text. It should give an example or hint of what you want the user to type in there (e.g. https://mysterious.com). Also, the color is so light you can barely see it.
The keyboard focus indicator on the links is almost non-existent. You should make it more obvious so that keyboard users know where the focus currently is at.
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no" /> This is a big no-no. Do not set user-scalable to ‘no’. Just get rid of it completely.
‘Dark Internet’ should be an <h1>. You should always have at least an <h1> header on your page.
I know it may not seem like a problem, but the light green text on white background does not have enough color contrast to be accessible. You can check your contrast levels at https://webaim.org/resources/contrastchecker/