How do you hide and unhide all columns in an Excel worksheet?

You can hide and unhide all columns in an Excel worksheet as shown in the following images:

I will hide all columns in HideAll.xlsx by clicking in the corner as shown. All cells are highlighted.

Now I go to the VIEW menu and click Hide.

Now everything is hidden. Notice even the worksheet name.

 Now I go back to VIEW and click on View to activate the Unhide submenu item.

 I click the Unhide button and I get the window for unhiding where I can choose to unhide the file.

Click on HideAll.xlsx. The HideAll.xlsx is displayed showing all columns and rows.