Update settings button on tokens page (#5085)

# Motivation

The icon buttons that use the ripple-effect look good in the dark theme
when focused or active (eg. after mouse down), but are too dim in the
light theme. This happens because, in the light theme, the button’s
background becomes dark when focused, and the icon color is also dark.

After updates in the gix-component
(dfinity/gix-components#452), it becomes
possible to provide the text color to the icon button with the ripple
effect. Here, we update the remaining button (settings) to look good
when pressed in the light theme.

# Changes

- Explicitly set the text color for the settings button to ensure it
looks good when pressed in the light theme.

# Screenshots

## Before

<img width="161" alt="image"
src="https://github.com/dfinity/nns-dapp/assets/98811342/baa4e160-0e3c-496e-b432-75c1a529be45">

## After

<img width="203" alt="image"
src="https://github.com/dfinity/nns-dapp/assets/98811342/a595524c-fe2d-4b4a-9512-cdbc64bb6564">

frontend/src/lib/pages/Tokens.svelte

@@ -90,11 +90,11 @@
   .settings-button {
     --content-color: var(--text-description);
 
-    @include effect.ripple-effect(--primary-tint);
+    @include effect.ripple-effect(--primary-tint, var(--primary-contrast));
 
     &:focus {
       background: var(--primary-tint);
-      @include effect.ripple-effect(--primary-tint);
+      @include effect.ripple-effect(--primary-tint, var(--primary-contrast));
     }
   }