gtk3: Fix oval circular buttons

Fixes: #103

Author: jnsh

common/gtk-3.0/3.24/sass/_common.scss

@@ -3189,9 +3189,9 @@ colorchooser .popover.osd { border-radius: 3px; }
 button.circular,
 button.circular-button {
   padding: 0;
-  min-width: 16px;
+  min-width: 24px;
   min-height: 24px;
-  padding: 2px 6px;
+  padding: 2px;
   border-radius: 50%;
   -gtk-outline-radius: 50%;