Here is section template mock up from JoeK4628, where the blue bar indicates the resizable control.

Hi, Can you tell us more about the use case? Meaning, where does this UI appear?  In the main work area or in a modal from a local action or in a case utility? What is it displaying?

Also, what happens as you keep shrinking one column? Is there a min-width to keep the column from being shrunk too small where fields no longer look good?

Is app built with the UI-Kit theme or Cosmos UI theme?

The reason I'm asking is because it seems like you're trying to solve a problem with having enough room for content.  Sometimes there's an alternative design to solve that without building a shrinkable column.

Generally, certainly this UI can be built by creating a custom design template (saved in application ruleset) with a bit of CSS.  

Sam

there is no such template available OTB in the end user portal but it is possible to build one relatively easily - it would require a few lines of JS to make it work. I would not recommend to use a screenlayout - the screenlayout is intend to be used for the whole portal layout and can only be dropped inside a harness.