Polypane automatically detects the width-based breakpoints defined in your CSS. You can create panes for each breakpoint by clicking the breakpoints button in the top right of the screen, or by pressing
cmd/ctrl b. These panes are ordered ascending by width (smallest first)
Inside the button you can see how many responsive sizes are defined in your CSS (and thus how much panes are created). This corresponds to the number of unique widths. Polypane adds panes at the beginning and end of the list if it detects that your CSS is also applied outside of these bounds.
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