HeatMap AdAptive layout -to change column widths

Hi Love this theme HeatMap AdAptive
Re Layout options, I have chosen three columns and the left column by default is narrower than the right column. I want to make both same size.
I only have the free version but didnt want to have to upgrade, just to change the default width of left column.
Can anyone tell me where I could change the columns width to be same each sidebar? I would expect to leave the maximum width the same, but all columns need to be re-stated for their new width to accommodate left column to be made wider.
In this free version there does not appear to be a custom css – so what code should I put in, and where?
Many thanks