This is just a tiny change i think would improve the vertical tabs.
Current State: To close the tab it needs to be expanded, expansion only happens when hovering the tab icon and than you have to move the mouse over the x to close it. Switching x button to the left of the tab icon would allow for faster closing of tabs, for Desktops it might be barely noticeable but on a laptop with a touch pad would be an improvement.
Since this might be locked to the UI used on the horizontal tabs, an alternative would be to hide the tab text in vertical and have the tittle show in a “balloon”. This way the x would be right next to the icon reducing the space taken during vertical tab expansion.