[simple theme] selection ui with border

* remove vim arrow
* add 1rem padding to results
* add 0.2rem left border to vim selected article
* set column gap to 1.2rem and make search bar in line with results
* put 10px border-radius selected article
* result article: 0.125rem margin on tablet and esktop; 1rem margin on phone

searx/static/themes/simple/src/less/mixins.less

@@ -16,6 +16,12 @@
   border-radius: @radius;
 }
 
+.rounded-right-corners (@radius: 0 10px 10px 0) {
+  -webkit-border-radius: @radius;
+  -moz-border-radius: @radius;
+  border-radius: @radius;
+}
+
 // disable user selection
 .disable-user-select () {
   -webkit-touch-callout: none;