[FIX] web: fix wrong padding css rule

The css rule I introduced in 737ba55 was poorly written, my bad.

addons/web/static/src/scss/fields.scss

@@ -32,11 +32,6 @@
         text-align: inherit;
     }
 
-    // Selection fields
-    &, select.o_input {
-        padding: 1px;  // Other inputs get a 1px padding automatically added by the browsers but selects do not
-    }
-
     // Block fields
     &.note-editor, &.oe_form_field_html, &.oe_form_field_html_text, &.oe_form_field_text, &.o_field_domain, &.o_graph_linechart, &.o_graph_barchart {
         display: block;
@@ -455,3 +450,8 @@ button.o_field_float_toggle {
     width: 100%;
     text-align: center;
 }
+
+// Selection fields
+select.o_field_widget.o_input {
+    padding: 1px;  // Other inputs get a 1px padding automatically added by the browsers but selects do not
+}