Specifying width for matrix columns

I am using Matrix widget (https://appstore.home.mendix.com/link/app/112555/). My matrix has first column with a relatively long text (30% of screen), following by a short note (10% of screen), and then a number of tiny columns which should be 3 characters or so wide. How can I control width of my columns? Do I somehow achieve this via CSS associated with matrix columns? I applied the following style to matrix columns .gl-matrix-narrow{width:5%;} with no visible effect.   MX 8.18.1
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