How to align the border with absolute positioning?

Question

css

A little stuck, the next question.
I have a table where the first column is static at position:absolute; , other columns scroll if necessary.
The problem is the border of the first column (border-right for th elements) - it needs to be made the same height as the borders for other columns (border-left for td elements).
I tried using the th height value - if you set width:100% as it is now, then the cells take up an excessively large height and the border goes deep down to the end of the page.
And if you set width: auto, then the border goes with gaps where the content of the right columns is higher in height than the content of the left column.
I seem to be missing something very simple, but I can't figure out what...
I just took the structure one by one, there is practically no possibility to change something in the code.