We shouldn't let the core render the `.content` class, so once we use custom layout in the default theme, the styles of default theme will pollute the styles of custom layout.

This reverts commit f04adbf1.

This reverts commit 760f90b9.

This reverts commit cab5b831.

fix($core): failed to load theme when using "layouts/Layout.vue" as entry file (close: #1563) (#1564)

Indent closing tag `</div>` at line 429.

ref: https://github.com/facebook/jest/pull/7687

fix($core): use directory name to compute slug if filename is readme or index (close: #1443) (#1535)