Fix Inline blocks style of two columns in the off-canvas

I noticed an issue with Inline Block Styles after updating to the newest version of the module.

When adding a new custom block (edit layout -> Add block -> Create custom block), the buttons are all stacked in a single column (they used to be 2 columns). The "Create custom block" button is also extending too far to the right, which is probably related, but not a major issue (unless it affects something else).