Checker bar and background pattern
Two decorative touches for the panel: a checkered strip across the top and a faint grid behind the board.
Two optional flourishes, each a toggle plus a colour.
Checker bar
A checkered strip flush across the top edge of the panel. It reads as playful and slightly retro, and it is the fastest way to make a plain panel look designed. Set the checker colour; the gaps show the panel background through.
Square pattern
A faint grid of squares over the panel background. Set the line colour. Keep it close to the panel colour: this should be texture you notice second, not a grid you notice first.
Using them together
Both at once works if the colours are restrained. Both at once in high contrast reads as busy and pulls attention away from the cards, which are the thing you want people looking at.
If you are unsure, pick one.
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