fixes #4118: responsive modal gets width auto and improved positioning for narrower widths

docs/assets/css/bootstrap-responsive.css

@@ -835,6 +835,17 @@
     display: inline-block;
     width: auto;
   }
+  .modal {
+    position: fixed;
+    top: 20px;
+    right: 20px;
+    left: 20px;
+    width: auto;
+    margin: 0;
+  }
+  .modal.fade.in {
+    top: auto;
+  }
 }
 
 @media (max-width: 480px) {
@@ -866,15 +877,9 @@
     padding-left: 10px;
   }
   .modal {
-    position: fixed;
     top: 10px;
     right: 10px;
     left: 10px;
-    width: auto;
-    margin: 0;
-  }
-  .modal.fade.in {
-    top: auto;
   }
   .modal-header .close {
     padding: 10px;

less/responsive-767px-max.less

@@ -84,6 +84,17 @@
     width: auto;
   }
 
+  // Modals
+  .modal {
+    position: fixed;
+    top:   20px;
+    left:  20px;
+    right: 20px;
+    width: auto;
+    margin: 0;
+    &.fade.in { top: auto; }
+  }
+
 }
 
 
@@ -133,13 +144,9 @@
 
   // Modals
   .modal {
-    position: fixed;
     top:   10px;
     left:  10px;
     right: 10px;
-    width: auto;
-    margin: 0;
-    &.fade.in { top: auto; }
   }
   .modal-header .close {
     padding: 10px;