Tint strength and blur strength values not stored correctly

[Laqco]

use GitHub reactions 👍 to show that you are affected by the same issue. Please don't comment if you have no relevant information to add!

• This is not a feature request
• This is not an image-provider request
• I have searched the issuetracker if the issue is not already reported.

Describe the bug:
When trying to change tint strength or blur strength in the Admin/Theming settings, the backrgound appearance doesn't change and, after a page reload, the sliders are back to their default values.

To Reproduce:

1. Turn on tinting.
2. Try to change tint strength and/or blur strength in Admin/Theming settings.

Expected behavior:
Background gets updated accordingly and sliders store correct values.

Server:

• Nextcloud version: 31.0.10
• Splash-App version: 3.1.0

Additional Information:
These two lines always set the returned value to the default value (30 and 0).

unsplash/templates/settings/admin.php

Line 131 in ff2ac67

value="<?= $_['styleStrengthColor'] ? $_['styleStrengthColor'] : 30 ?>"

unsplash/templates/settings/admin.php

Line 138 in ff2ac67

value="<?= $_['styleStrengthBlur'] ? $_['styleStrengthBlur'] : 0 ?>">

[Laqco]

I found a solution using CustomCSS:

html {
    background-color: unset;
}
body {
  backdrop-filter: blur(5px);
}

While trying, I found out that this App only sets the body's backdrop-filter:

unsplash/lib/Controller/CssController.php

Line 151 in ff2ac67

$css .= "backdrop-filter: blur($blurStrenghtpx);";

This only applies the blur to the login screen, unless the html's background-color is unset (which is defined in the login screen's CSS).