The indicator line below the tab label should always correspond to the selected tab.
In a number of cases the first tab may not be the initially selected one:
In Chrome: when you select a tab other than the first, click a link to navigate to another page, then use the back command in the browser to go back. Chrome will remember the state of the form controls.
In Firefox: same as for Chrome, plus in addition if you select a tab other than the first, then refresh the page.
The result is that the indicator line is shown for the wrong element:
Steps to reproduce
Generate the documentation for mkdocs-material using the public non-insiders version of the theme.
Go to the content tabs page.
Select a tab other than the first.
Click a link to go to another page.
Click the back button.
Observe that the indicator line displays incorrectly.
Fixed in 6976b9f. Tricky stuff. The interesting fact is that when going back, the browser will set the active tab to the previous tab asynchronously, which btw. is a nice side effect of leveraging form fields. Previous to this commit, the indicator was always set to the first tab on load. Now, content tabs are mounted asynchronously (actually the first time I used the subscribeOn operator after doing RxJS for more than two years now), which should correctly determine the active tab.