MDL-56016 theme_boost: Add plain preset for plain Moodle & Bootstrap

theme/boost/lang/en/theme_boost.php

@@ -38,6 +38,7 @@ $string['preset_desc'] = 'Pick a preset to broadly change the look of the theme.
 $string['presetdefault'] = 'Default';
 $string['presetflatly'] = 'Flatly';
 $string['presetpaper'] = 'Paper';
+$string['presetplain'] = 'Plain';
 $string['presetreadable'] = 'Readable';
 $string['rawscss'] = 'Raw SCSS';
 $string['rawscss_desc'] = 'Use this field to provide SCSS code which will be injected at the end of the the stylesheet.';

theme/boost/scss/preset-plain.scss

@@ -0,0 +1,12 @@
+/**
+ * Plain preset file.
+ *
+ * This preset is plain Moodle & Bootstrap and must not contain anything else.
+ *
+ * To create your own preset file:
+ * - Duplicate this file and rename it, for instance to preset-apple.scss.
+ * - In settings.php, find the references to 'plain', duplicate them and rename
+ *   them to 'apple'. (Look around the choices for 'theme_boost/preset').
+ */
+
+@import "moodle";

theme/boost/settings.php

@@ -32,6 +32,7 @@ if ($ADMIN->fulltree) {
     $description = get_string('preset_desc', 'theme_boost');
     $choices = [
         // A file named 'preset-' . key . '.scss' is expected.
+        'plain' => get_string('presetplain', 'theme_boost'),
         'default' => get_string('presetdefault', 'theme_boost'),
         'flatly' => get_string('presetflatly', 'theme_boost'),
         'paper' => get_string('presetpaper', 'theme_boost'),