Hi summer lady,
You need to press Shift key and then press underscore key on the keyboard to place an underscore. Ctrl and plus (+) key increases the size and appearance of page, file and folder icons and similarly Ctrl and minus (-) key decreases the size and appearance of page, file and folder icons.
Have a look at the following article link or more information on Keyboard shortcuts:
Hope this helps.
Thanks and Regards, Santosh Y – Microsoft Support
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