Board Thread:Support Requests - Getting Technical/@comment-30760490-20200830080325/@comment-32704847-20200830130312

The right thing to do there is to apply a CSS rule that nullifies the bolder weight of the font on selected tabs, because tabs with more text will always have more additional width when selected than those with less text. This cause the total width of the nav to vary according to which tab is selected. And that may cause the disgusting line break. Use color of text and background color to highlight tabs; never font weight (example).

If not you'd have to be careful on each nav to reduce the total amount of text there. For example, in your page, couldn't you replace "Maomao's Diary" with simply "Diary"? The box is for her, after all.