Remove black border on buttons in IE7:

1. Removed borders on .btn and increased line-height 2px to compensate
2. Set buttons to use the endColor of the gradient as the background-color by default for extra contrast between button and background
3. Set a 5% darker background-color on hover of buttons just for IE7

less/buttons.less

@@ -28,6 +28,10 @@
 
   // Give IE7 some love
   .ie7-restore-left-whitespace();
+
+  /* Remove the border to prevent IE7's black border on input:focus */
+  *border: 0;
+  *line-height: 20px;
 }
 
 // Hover state
@@ -35,6 +39,7 @@
   color: @grayDark;
   text-decoration: none;
   background-color: darken(@white, 10%);
+  *background-color: darken(@white, 15%); /* Buttons in IE7 don't get borders, so darken on hover */
   background-position: 0 -15px;
 
   // transition is only when going to hover, otherwise the background

less/mixins.less

@@ -427,10 +427,12 @@
   // gradientBar will set the background to a pleasing blend of these, to support IE<=9
   .gradientBar(@startColor, @endColor);
   .reset-filter();
+  *background-color: @endColor; /* Darken IE7 buttons by default so they stand out more given they won't have borders */
 
   // in these cases the gradient won't cover the background, so we override
   &:hover, &:active, &.active, &.disabled, &[disabled] {
     background-color: @endColor;
+    *background-color: darken(@endColor, 5%);
   }
 
   // IE 7 + 8 can't handle box-shadow to show active, so we darken a bit ourselves