fix(VTooltip, VSnackbar): increase contrast on dark theme (#21184)

Author: J-Sek

Diff for: packages/vuetify/src/composables/__tests__/__snapshots__/theme.spec.ts.snap

@@ -131,9 +131,9 @@ exports[`createTheme > should create style element 1`] = `
       --v-theme-surface-bright-overlay-multiplier: 2;
       --v-theme-surface-light: 66,66,66;
       --v-theme-surface-light-overlay-multiplier: 1;
-      --v-theme-surface-variant: 163,163,163;
+      --v-theme-surface-variant: 200,200,200;
       --v-theme-surface-variant-overlay-multiplier: 2;
-      --v-theme-on-surface-variant: 66,66,66;
+      --v-theme-on-surface-variant: 0,0,0;
       --v-theme-primary: 33,150,243;
       --v-theme-primary-overlay-multiplier: 2;
       --v-theme-primary-darken-1: 39,124,193;

Diff for: packages/vuetify/src/composables/theme.ts

@@ -159,8 +159,8 @@ function genDefaults () {
           surface: '#212121',
           'surface-bright': '#ccbfd6',
           'surface-light': '#424242',
-          'surface-variant': '#a3a3a3',
-          'on-surface-variant': '#424242',
+          'surface-variant': '#c8c8c8',
+          'on-surface-variant': '#000000',
           primary: '#2196F3',
           'primary-darken-1': '#277CC1',
           secondary: '#54B6B2',