paper: focused checkboxes have colored border, closes #505

paper/_bootswatch.scss

@@ -316,6 +316,10 @@ input[type="checkbox"],
     outline: none;
   }
 
+  &:focus:after {
+    border-color: $brand-primary;
+  }
+
   &:after {
     content: "";
     display: block;

paper/bootstrap.css

@@ -7296,6 +7296,11 @@ input[type="checkbox"]:focus,
 .checkbox-inline input[type="checkbox"]:focus {
   outline: none;
 }
+input[type="checkbox"]:focus:after,
+.checkbox input[type="checkbox"]:focus:after,
+.checkbox-inline input[type="checkbox"]:focus:after {
+  border-color: #2196f3;
+}
 input[type="checkbox"]:after,
 .checkbox input[type="checkbox"]:after,
 .checkbox-inline input[type="checkbox"]:after {

paper/bootswatch.less

@@ -316,6 +316,10 @@ input[type="checkbox"],
     outline: none;
   }
 
+  &:focus:after {
+    border-color: @brand-primary;
+  }
+
   &:after {
     content: "";
     display: block;