Don't add style provider before startup

Should fix #1267

src/book-viewer.js

@@ -19,7 +19,7 @@ import { AnnotationPopover, importAnnotations, exportAnnotations } from './annot
 import { SelectionPopover } from './selection-tools.js'
 import { ImageViewer } from './image-viewer.js'
 import { formatAuthors, makeBookInfoWindow } from './book-info.js'
-import { themes, invertTheme } from './themes.js'
+import { themes, invertTheme, themeCssProvider } from './themes.js'
 import { dataStore } from './data.js'
 
 // for use in the WebView
@@ -489,6 +489,8 @@ export const BookViewer = GObject.registerClass({
             this._zoom_button.label = format.percent(webView.zoom_level))
         this._zoom_button.label = format.percent(this._view.webView.zoom_level)
 
+        Gtk.StyleContext.add_provider_for_display(Gdk.Display.get_default(),
+            themeCssProvider, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
         let lastThemeClass
         const recolorUI = view => {
             const theme = themes.find(theme => theme.name === view.theme) ?? themes[0]

src/themes.js

@@ -1,6 +1,5 @@
 import Gtk from 'gi://Gtk'
 import GLib from 'gi://GLib'
-import Gdk from 'gi://Gdk'
 import { gettext as _ } from 'gettext'
 import * as utils from './utils.js'
 
@@ -73,7 +72,7 @@ for (const { file, name } of utils.listDir(pkg.configpath('themes'))) try {
     console.error(e)
 }
 
-const themeCssProvider = new Gtk.CssProvider()
+export const themeCssProvider = new Gtk.CssProvider()
 themeCssProvider.load_from_data(`
     .theme-container .card {
         padding: 9px;
@@ -107,10 +106,6 @@ themeCssProvider.load_from_data(`
         }
     `
 }).join(''), -1)
-Gtk.StyleContext.add_provider_for_display(
-    Gdk.Display.get_default(),
-    themeCssProvider,
-    Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
 
 export const invertTheme = ({ light, dark }) => ({ light, dark, inverted: {
     fg: utils.invertColor(dark.fg),