In the "Accessibility" section, select Manage accessibility features. Under "Display," turn on Enable docked magnifier. To choose your zoom level, next to "Docked zoom level," select Down arrow . At the top of your screen, you'll see the zoomed in area.

You have enabled the "Docked Magnifier"

https://support.google.com/chromebook/answer/6320705?hl=en

Magnify part of your screen

You’ll see the magnified section in the top third of your screen. Your default screen will show underneath. To quickly magnify the top section of your screen, press Ctrl + Search + d, or follow the steps below.

1. At the bottom right, select the time. Or press Alt + Shift + s.
2. Select Settings .
3. At the bottom, select Advanced.
4. In the "Accessibility" section, select Manage accessibility features.
5. Under "Display," turn on Enable docked magnifier.
6. To choose your zoom level, next to "Docked zoom level," select Down arrow .
7. At the top of your screen, you’ll see the zoomed in area. To change what's magnified, move your cursor.