Think of your layout in percent of the screen width at different sizes.
Note that there is a maximum width for content. This helps with readability.
Section 1
Column 1
Column 2
Section 2
Column 1
Column 2
Section 3
Column 1
Column 2
Column 3
Column 4
Section 4
1em - default
1.25em
1.5em
1.75em
2em