fix(theme): stabilize palette selector without instant navigation (#2706)

Author: claudiacodacy

theme/partials/palette.html

@@ -11,4 +11,8 @@
       </label>
     {% endif %}
   {% endfor %}
+  <span class="docs-palette__fallback" aria-hidden="true">
+    <span class="docs-palette__fallback-button docs-palette__fallback-button--light md-icon">{{ icon("moon-outline") }}</span>
+    <span class="docs-palette__fallback-button docs-palette__fallback-button--dark md-icon">{{ icon("sunny-outline") }}</span>
+  </span>
 </form>