Floating Lyrics
The current line on a panel above every window, that clicks fall straight through.
The default surface, and the one most people keep. A panel showing the line being sung, on top of every window, that you can read without stopping what you are doing.
Toggle it with Cmd/Ctrl + Shift + L, from the tray, or in Settings › Floating Lyrics.

Clicks fall through it
By default the panel is not there as far as your mouse is concerned. Click where it is and the click lands in the window behind — the editor, the browser, the game. It never steals focus and never interrupts.
The exceptions are deliberate. While the pointer is over it, the panel takes clicks for its own controls and for a Search or Retry button when lyrics could not be found, because a button you cannot press is not a button.
Moving it
Drag it. While the position is unlocked, the panel takes the mouse under the pointer so it can be picked up, and goes back to ignoring clicks once you let go.
Lock position pins it. Pinning also turns click-through on: a locked panel is something to read, not to handle.
Reset position in Settings puts it back where it started, which is quicker than hunting for a panel dragged onto a monitor you no longer have.
Hide while the mouse is over it
An alternative to click-through for people who would rather the panel simply got out of the way. With it on, moving the pointer over the panel fades it out entirely and lets every click through. It has no hover controls while it is on — that is the trade — so turn it off to reach them.
One line or two
Single-line mode shows only the line playing now. A line too long for the panel walks across once and stops, rather than being cut off mid-word — Scroll long lines controls that, and it pauses with playback and respects Reduced Motion.
With single-line off, the next line shows underneath, dimmer.
Appearance

Font size, weight, alignment and opacity, a blurred backdrop, and a tint taken from the album art. The current line's colours come from Lyric Highlight, which is shared with every other surface, so you set them once.