diff --git a/src/mixins/ThemingMixin.js b/src/mixins/ThemingMixin.js
new file mode 100644
index 00000000..205a6948
--- /dev/null
+++ b/src/mixins/ThemingMixin.js
@@ -0,0 +1,130 @@
+// import {
+//   LoadExternalTheme,
+//   ApplyLocalTheme,
+//   ApplyCustomVariables,
+// } from '@/utils/ThemeHelper';
+import { builtInThemes, localStorageKeys, mainCssVars } from '@/utils/defaults';
+import Keys from '@/utils/StoreMutations';
+import ErrorHandler from '@/utils/ErrorHandler';
+
+const ThemingMixin = {
+  data: () => ({
+    selectedTheme: '',
+    // themeHelper: new LoadExternalTheme(),
+  }),
+  computed: {
+    themeFromStore() {
+      return this.$store.getters.theme;
+    },
+    appConfig() {
+      return this.$store.getters.appConfig;
+    },
+    extraThemeNames() {
+      const userThemes = this.appConfig?.cssThemes || [];
+      if (typeof userThemes === 'string') return [userThemes];
+      return userThemes;
+    },
+    /* If user specified external stylesheet(s), format and return */
+    externalThemes() {
+      const availibleThemes = {};
+      if (this.appConfig?.externalStyleSheet) {
+        const externals = this.appConfig.externalStyleSheet;
+        if (Array.isArray(externals)) {
+          externals.forEach((ext, i) => {
+            availibleThemes[`External Stylesheet ${i + 1}`] = ext;
+          });
+        } else if (typeof externals === 'string') {
+          availibleThemes['External Stylesheet'] = this.appConfig.externalStyleSheet;
+        } else {
+          ErrorHandler('External stylesheets must be of type string or string[]');
+        }
+      }
+      return availibleThemes;
+    },
+    /* Combines all theme names (builtin and user defined) together */
+    themeNames() {
+      const externalThemeNames = Object.keys(this.externalThemes);
+      return [...this.extraThemeNames, ...externalThemeNames, ...builtInThemes];
+    },
+  },
+  watch: {
+    /* When theme in VueX store changes, then update theme */
+    themeFromStore(newTheme) {
+      this.selectedTheme = newTheme;
+      this.updateTheme(newTheme);
+    },
+  },
+  methods: {
+    /* Called when user changes theme through the UI
+     * Updates store, which will in turn update theme through watcher
+     */
+    themeChanged() {
+      this.$store.commit(Keys.SET_THEME, this.selectedTheme);
+      this.updateTheme(this.selectedTheme);
+    },
+    /**
+     * Gets any custom styles the user has applied, wither from local storage, or from the config
+     * @returns {object} An array of objects, one for each theme, containing kvps for variables
+     */
+    getCustomColors() {
+      const localColors = JSON.parse(localStorage[localStorageKeys.CUSTOM_COLORS] || '{}');
+      const configColors = this.appConfig.customColors || {};
+      return Object.assign(configColors, localColors);
+    },
+    /* Gets user custom color preferences for current theme, and applies to DOM */
+    applyCustomVariables(theme) {
+      mainCssVars.forEach((vName) => { document.documentElement.style.removeProperty(`--${vName}`); });
+      const themeColors = this.getCustomColors()[theme];
+      if (themeColors) {
+        Object.keys(themeColors).forEach((customVar) => {
+          document.documentElement.style.setProperty(`--${customVar}`, themeColors[customVar]);
+        });
+      }
+    },
+    /* Sets the theme, by updating data-theme attribute on the html tag */
+    applyLocalTheme(newTheme) {
+      const htmlTag = document.getElementsByTagName('html')[0];
+      if (htmlTag.hasAttribute('data-theme')) htmlTag.removeAttribute('data-theme');
+      htmlTag.setAttribute('data-theme', newTheme);
+    },
+    /* Determines if a given theme is local / not a custom user stylesheet */
+    isThemeLocal(themeToCheck) {
+      const localThemes = [...builtInThemes, ...this.extraThemeNames];
+      return localThemes.includes(themeToCheck);
+    },
+    /* Updates theme. Checks if the new theme is local or external,
+    and calls appropirate updating function. Updates local storage */
+    updateTheme(newTheme) {
+      // this.themeHelper.theme = newTheme;
+      if (newTheme.toLowerCase() === 'default') {
+        this.resetToDefault();
+      } else if (this.isThemeLocal(newTheme)) {
+        this.applyLocalTheme(newTheme);
+      }
+      this.applyCustomVariables(newTheme);
+    },
+    /* Removes any applied themes */
+    resetToDefault() {
+      document.getElementsByTagName('html')[0].removeAttribute('data-theme');
+    },
+    initializeTheme() {
+      const initialTheme = this.themeFromStore;
+      this.selectedTheme = initialTheme;
+      const hasExternal = this.externalThemes && Object.entries(this.externalThemes).length > 0;
+
+      if (this.isThemeLocal(initialTheme)) {
+        this.updateTheme(initialTheme);
+      } else if (hasExternal) {
+        const added = Object.keys(this.externalThemes).map(
+          name => this.themeHelper.add(name, this.externalThemes[name]),
+        );
+        // Once, added, then apply users initial theme
+        Promise.all(added).then(() => {
+          this.updateTheme(initialTheme);
+        });
+      }
+    },
+  },
+};
+
+export default ThemingMixin;