You can easily format the karaoke text font/size/color using the font panel ("Show Fonts" from the "View > Font" menu). Formatting is applied to both text, chords and markers. Chords and markers visibility can be toggled with the "View > Chords" and "View > Markers" menu items.
If the "Auto Size" option is checked, QMidi resizes the text accordingly to the window height so that a constant number of lines are viewed. The chords can then be independently sized by dragging the text/chord divider.
When opened, styled text with the same color as background is automatically set to white/black, depending on the background color.
With the "View > Background Image" menu, you can add a background image to your karaoke window. You may also drag an image from the finder to do this.
You can also manually link an image to a single media file:
If a karaoke file has been created on other platforms, accented characters are not displayed correctly using the default encoding. To fix this problem, QMidi allows you to choose the appropriate text encoding for any karaoke file and to save your settings within the playlist/library. You can change the default encoding in the Settings dialog.
During this operation, a QMidi project will be created with the same base name in the media file's directory.

NB: You should never edit synced lyrics in Edit Mode because this may invalidate sync information.
The safe way to edit existing lyrics, chords or markers is the following:

The "CR" column is used to add/remove line breaks.
The behavior of the "+" button depends on the current selection state:
button at bottom to enable sync mode.You can of course do step 4 while the player is stopped. It is not necessary to synchronize the entire text at once: you can adjust the row's position at any time by rewinding and clicking it at the right time. All these actions may be undone using the "Edit > Undo" menu.
Tips: Option-Click a row to move the playhead at the corresponding time; Shift-click to move all subsequent rows.
Enter the synchronize mode and click the "Edit" (pencil) button to enable manual editing.

The "Time" column is formatted as measure:beat:tick (for MIDI files and media files with a linked MIDI file) or HH:MM:SS.MS.
Use these menu items if you want to synchronize word by word or line by line.
Applies the specified text transformation to the selected rows.
Opens the shift time dialog.
Opens the adjust tempo dialog. You can here lengthen or shorten the duration of the selected time range.
Opens the quantize dialog.
Reloads the sync data (lyrics, chords or markers) embedded in the media file, if any.
Chords must use the standard notation format "A#m7/E", where the first letter is the chord name (capitals letters A-G) , the second is the accidental (#, b or white space), followed by the chord description. The bass note may also be added at the end, separated the "/" character.
Valid chords examples:
"B m7"
"Gbsus4"
"D#/F" --> bass note is F
"E/F#" --> bass note is F#