Make the border-radius on input-groups to be overrides instead of resets on every size.

docs/assets/css/bootstrap.css

@@ -1637,20 +1637,11 @@ select:focus:invalid:focus {
 .input-group-btn,
 .input-group input {
   display: table-cell;
-  /*margin: 0;*/
-
-  border-radius: 0;
-}
-
-.input-group-addon.input-small,
-.input-group-btn.input-small,
-.input-group input.input-small {
-  border-radius: 0;
 }
 
-.input-group-addon.input-large,
-.input-group-btn.input-large,
-.input-group input.input-large {
+.input-group-addon:not(:first-child):not(:last-child),
+.input-group-btn:not(:first-child):not(:last-child),
+.input-group input:not(:first-child):not(:last-child) {
   border-radius: 0;
 }
 
@@ -1669,6 +1660,7 @@ select:focus:invalid:focus {
   text-shadow: 0 1px 0 #fff;
   background-color: #eeeeee;
   border: 1px solid #ccc;
+  border-radius: 4px;
   -webkit-box-sizing: border-box;
      -moz-box-sizing: border-box;
           box-sizing: border-box;
@@ -1677,29 +1669,21 @@ select:focus:invalid:focus {
 .input-group-addon.input-small {
   padding: 2px 10px;
   font-size: 11.9px;
+  border-radius: 3px;
 }
 
 .input-group-addon.input-large {
   padding: 11px 14px;
   font-size: 17.5px;
+  border-radius: 6px;
 }
 
 .input-group input:first-child,
-.input-group-addon:first-child {
-  border-bottom-left-radius: 4px;
-  border-top-left-radius: 4px;
-}
-
-.input-group input:first-child.input-small,
-.input-group-addon:first-child.input-small {
-  border-bottom-left-radius: 3px;
-  border-top-left-radius: 3px;
-}
-
-.input-group input:first-child.input-large,
-.input-group-addon:first-child.input-large {
-  border-bottom-left-radius: 6px;
-  border-top-left-radius: 6px;
+.input-group-addon:first-child,
+.input-group-btn:first-child > .btn:first-child,
+.input-group-btn:first-child > .dropdown-toggle:first-child {
+  border-top-right-radius: 0;
+  border-bottom-right-radius: 0;
 }
 
 .input-group-addon:first-child {
@@ -1707,21 +1691,11 @@ select:focus:invalid:focus {
 }
 
 .input-group input:last-child,
-.input-group-addon:last-child {
-  border-top-right-radius: 4px;
-  border-bottom-right-radius: 4px;
-}
-
-.input-group input:last-child.input-small,
-.input-group-addon:last-child.input-small {
-  border-top-right-radius: 3px;
-  border-bottom-right-radius: 3px;
-}
-
-.input-group input:last-child.input-large,
-.input-group-addon:last-child.input-large {
-  border-top-right-radius: 6px;
-  border-bottom-right-radius: 6px;
+.input-group-addon:last-child,
+.input-group-btn:last-child > .btn:last-child,
+.input-group-btn:last-child > .dropdown-toggle {
+  border-bottom-left-radius: 0;
+  border-top-left-radius: 0;
 }
 
 .input-group-addon:last-child {
@@ -1736,7 +1710,6 @@ select:focus:invalid:focus {
 .input-group-btn > .btn {
   position: relative;
   float: left;
-  border-radius: 0;
 }
 
 .input-group-btn > .btn + .btn {
@@ -1748,42 +1721,6 @@ select:focus:invalid:focus {
   z-index: 2;
 }
 
-.input-group-btn:first-child > .btn:first-child,
-.input-group-btn:first-child > .dropdown-toggle:first-child {
-  border-bottom-left-radius: 4px;
-  border-top-left-radius: 4px;
-}
-
-.input-group-btn:first-child > .btn:first-child.btn-large,
-.input-group-btn:first-child > .dropdown-toggle:first-child.btn-large {
-  border-bottom-left-radius: 6px;
-  border-top-left-radius: 6px;
-}
-
-.input-group-btn:first-child > .btn:first-child.btn-small,
-.input-group-btn:first-child > .dropdown-toggle:first-child.btn-small {
-  border-bottom-left-radius: 3px;
-  border-top-left-radius: 3px;
-}
-
-.input-group-btn:last-child > .btn:last-child,
-.input-group-btn:last-child > .dropdown-toggle {
-  border-top-right-radius: 4px;
-  border-bottom-right-radius: 4px;
-}
-
-.input-group-btn:last-child > .btn:last-child.btn-large,
-.input-group-btn:last-child > .dropdown-toggle.btn-large {
-  border-top-right-radius: 6px;
-  border-bottom-right-radius: 6px;
-}
-
-.input-group-btn:last-child > .btn:last-child.btn-small,
-.input-group-btn:last-child > .dropdown-toggle.btn-small {
-  border-top-right-radius: 3px;
-  border-bottom-right-radius: 3px;
-}
-
 .form-inline input,
 .form-inline select,
 .form-inline textarea,

less/forms.less

@@ -407,12 +407,8 @@ select:focus:invalid {
 .input-group-btn,
 .input-group input {
   display: table-cell;
-  /*margin: 0;*/
-  border-radius: 0;
-  &.input-small {
-    border-radius: 0;
-  }
-  &.input-large {
+
+  &:not(:first-child):not(:last-child) {
     border-radius: 0;
   }
 }
@@ -435,40 +431,35 @@ select:focus:invalid {
   text-shadow: 0 1px 0 #fff;
   background-color: @gray-lighter;
   border: 1px solid #ccc;
+  border-radius: @border-radius-base;
 
 	&.input-small {
 	  padding: @padding-small;
 	  font-size: @font-size-small;
+    border-radius: @border-radius-small;
   }
-	&.input-large {
-		padding: @padding-large;
-		font-size: @font-size-large;
+  &.input-large {
+    padding: @padding-large;
+    font-size: @font-size-large;
+    border-radius: @border-radius-large;
 	}
 }
 
 // Reset rounded corners
 .input-group input:first-child,
-.input-group-addon:first-child {
-  .border-left-radius(@border-radius-base);
-  &.input-small {
-    .border-left-radius(@border-radius-small);
-  }
-  &.input-large {
-    .border-left-radius(@border-radius-large);
-  }
+.input-group-addon:first-child,
+.input-group-btn:first-child > .btn:first-child,
+.input-group-btn:first-child > .dropdown-toggle:first-child {
+  .border-right-radius(0);
 }
 .input-group-addon:first-child {
   border-right: 0;
 }
 .input-group input:last-child,
-.input-group-addon:last-child {
-  .border-right-radius(@border-radius-base);
-  &.input-small {
-    .border-right-radius(@border-radius-small);
-  }
-  &.input-large {
-    .border-right-radius(@border-radius-large);
-  }
+.input-group-addon:last-child,
+.input-group-btn:last-child > .btn:last-child,
+.input-group-btn:last-child > .dropdown-toggle {
+  .border-left-radius(0);
 }
 .input-group-addon:last-child {
   border-left: 0;
@@ -483,7 +474,6 @@ select:focus:invalid {
 .input-group-btn > .btn {
   position: relative;
   float: left; // Collapse white-space
-  border-radius: 0;
   + .btn {
     margin-left: -1px;
   }
@@ -494,29 +484,6 @@ select:focus:invalid {
   }
 }
 
-// Prepended buttons
-.input-group-btn:first-child {
-  // Round the left corners only
-  > .btn:first-child,
-  > .dropdown-toggle:first-child {
-    .border-left-radius(@border-radius-base);
-    &.btn-large { .border-left-radius(@border-radius-large); }
-    &.btn-small { .border-left-radius(@border-radius-small); }
-  }
-}
-
-// Appended buttons
-.input-group-btn:last-child {
-  // Round the right corners only
-  > .btn:last-child,
-  > .dropdown-toggle {
-    .border-right-radius(@border-radius-base);
-    &.btn-large { .border-right-radius(@border-radius-large); }
-    &.btn-small { .border-right-radius(@border-radius-small); }
-  }
-}
-
-
 
 // Inline forms
 // --------------------------------------------------