how to conditional format blank cells in excell
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Excel isn’t relevant here, but in LibreOffice Calc on for example cell A1 you go to menu Format → Conditional → Condition, as Condition 1 select Formula is and in the edit field enter ISBLANK(A1) and for Apply Style choose or create a style. If the condition is to be applied to a cell range enter the range under Cell Range (or select the range before invoking the dialog).