OptionGroup grouped in 3 columns

Hi, I’m brand new to a project that is using Vaadin 6.0.1 which can’t be upgraded right now unfortunately. I’m also new to Vaadin and have very limited knowledge of CSS. I’m trying to create a 3x12 OptionGroup section. I’ve modified the css as below, but that only puts the items in a horizontal format and looks messy when using a lot of values in the OptionGroup (see attached image).

.v-app .v-select-optiongroup .v-select-option {
display: inline-block;
white-space: nowrap;
}

All ideas are greatly appreciated!

13242.png

This can be solved by adding the below to the CSS

.v-app .v-select-optiongroup .v-select-option {
width: 33%;
min-width: 150px;
float: left;
}