[minnesota_bound]

View this example instead. Much simplier. I edit the 2nd link below to do away with most of the col- widths so instead of 12 I have 3 instead.
https://www.w3schools.com/css/tryit.asp?filename=tryresponsive_breakpoints

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Example of a layout. Modify then click on the Run button. Resize the browser window or move the center divider to see changes.
https://www.w3schools.com/css/tryit.asp?filename=tryresponsive_breakpoints

[minnesota_bound]

I cannot show my edits so ignore the link as the example by W3schools is too complicated. You can reduce their 12 columns to just 3.

IGNORE
Example of a layout. Modify then click on the Run button. Resize the browser window or move the center divider to see changes.
https://www.w3schools.com/css/tryit.asp?filename=tryresponsive_breakpoints