I'm using the Stylus extension for applying custom styles. It's available for Firefox, Chrome and Opera (see FAQ #1 in the link). There are other extensions available for applying custom styles but Stylus is probably the best of the bunch, and is open source.
Stylus :: add0n.com
https://add0n.com/stylus.htmlSteps to setup custom styles:
(specific to Stylus and Firefox but it should be similar across browsers)
1. Install Stylus
By default, the Stylus icon will be added to your toolbar (it's a S with green background). If not, add it, and it makes management simpler.
2. Click on the Stylus extension in the toolbar
3. Click the Manage button, to open the Stylus styles manager
4. Click the Write New Style button, in the left hand menu bar
5. Enter a name for the style (eg My FindMyPast)
6. Click the Import button and paste the code in the attachment (My FindMyPast.css.txt)
7. Click the Overwrite style button
8. Click the Save button, in the left hand menu bar
Your custom style should appear as in the attachment and it should be active. If you want to disable it or delete it, use either the Stylus toolbar menu or the Stylus Manager. Or just remove the Stylus extension completely.
Something to be aware of is that FindMyPast frequently change their page layouts so it's possible they'll change the names of the elements used in the viewer and break the custom styles. But if they do I'll notice and I'll update this thread.