Theia sidepanel tabbar

Hello,I found some styles in the ‘sidepanel.css’ file
.p-TabBar.theia-app-left .p-TabBar-tabLabel {
transform-origin: top left 0;
transform: rotate(-90deg) translateX(-100%);
}

.p-TabBar.theia-app-right .p-TabBar-tabLabel {
transform-origin: top left 0;
transform: rotate(90deg) translateY(-50%);
}
I want to confirm that this style leads to the use of hiddenContentNode in ‘tab-bar.ts’file? Do I need to check the phosphorjs source code to understand these details?