Use fixed width for ruleset tools containers

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/1033

src/css/popup-fenix.css

@@ -82,8 +82,8 @@ body.off #switch {
     box-sizing: border-box;
     display: flex;
     flex-direction: column;
-    flex-grow: 2;
     justify-content: space-evenly;
+    width: 25%;
     }
 .rulesetTools [id] {
     background-color: var(--bg-transient-notice);