adminlte 3.0.1 fixed the bug, that was fixed with this line

knoxfighter · knoxfighter · commit 0404f8856743 · 2020-01-29T15:44:19.000+01:00
diff --git a/ui/scss/customizations/buttons.scss b/ui/scss/customizations/buttons.scss
@@ -1,4 +1,3 @@
 .btn {
     border-radius: 0;
-    border: none;
 }
