It should be a mix of linear gradient and background image. You won’t make the linear gradient completely opaque so that the background image will be visible.
Something like: background: linear-gradient(to right, #275e67e0, #275e67e0), url("https://i.imgur.com/GPDYiK.jpg") no-repeat fixed center center;
You can add as many gradients you want…
Your form looks good though.