If Excel is not highlighting cells in the formula, enable 'Allow editing directly in cells' and 'Enable fill handle and cell drag-and-drop' in Excel options.

Adding a text to a cell in Excel using Formula requires use of ampersand operator, CONCAT function, or the LEFT, RIGHT, and LEN functions.

The default active cell format in Microsoft Excel isn't all that easy to see, but you can use this easy-to-implement code solution to change that.