Vertical line not visible in editor

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As the subject line says, the vertical line, which tells you if a line of code is too long, is not visible in the editor.  I have tried changing the number of characters before the vertical line to 20 in Spyder's preferences, but nothing has shown up.  In case it helps, I have included a screenshot.

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Ok.  I just tried the trusty quit and restart Spyder and the vertical line reappeared.