fixes #10024: Use negative margin to fix the border between button and input in input groups

dist/css/bootstrap.css

@@ -3791,6 +3791,14 @@ textarea.input-group-sm > .input-group-btn > .btn {
   white-space: nowrap;
 }
 
+.input-group-btn:first-child > .btn {
+  margin-right: -1px;
+}
+
+.input-group-btn:last-child > .btn {
+  margin-left: -1px;
+}
+
 .input-group-btn > .btn {
   position: relative;
 }

less/input-groups.less

@@ -113,6 +113,14 @@
 .input-group-btn {
   position: relative;
   white-space: nowrap;
+
+  // Negative margin to only have a 1px border between the two
+  &:first-child > .btn {
+    margin-right: -1px;
+  }
+  &:last-child > .btn {
+    margin-left: -1px;
+  }
 }
 .input-group-btn > .btn {
   position: relative;