best way to custom grid size

[craigcosmo]

I want to two columns, sizes are 9.5 and 2.5, what's the best way to achieve this?

[drmnk]

Hello, craigcosmo!
You can change width of columns with simple "flex" property (in column), which can take percents as value.
For your situation you can use (100/13)*2.5 = 19.23 % and 80.77%.

It's very important to set "flex" and values in every colums you want to resize;