fix(core): insert theme stylesheet first to allow overriding (framewo…

…rk7io#4219) (framework7io#4220)

* fix(theme): insert theme stylesheet first to allow overriding (framework7io#4219)

* Update app-class.js

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Co-authored-by: Vladimir Kharlampidi <nolimits4web@gmail.com>

src/core/components/app/app-class.js

@@ -138,7 +138,7 @@ class Framework7 extends Framework7Class {
     const document = getDocument();
     if (!app.colorsStyleEl) {
       app.colorsStyleEl = document.createElement('style');
-      document.head.appendChild(app.colorsStyleEl);
+      document.head.prepend(app.colorsStyleEl);
     }
 
     app.colorsStyleEl.textContent = app.utils.colorThemeCSSStyles(app.colors);