Support color customization from the admin (#2338)

* Add user-customizable theming. Closes #1915

* Prettified Code!

* Add user-customizable theming. Closes #1915

* Add explicit color for page content background

* Prettified Code!

Co-authored-by: gabek <gabek@users.noreply.github.com>

test/automated/api/configmanagement.test.js

@@ -8,6 +8,11 @@ const offlineMessage = randomString();
 const pageContent = `<p>${randomString()}</p>`;
 const tags = [randomString(), randomString(), randomString()];
 const latencyLevel = Math.floor(Math.random() * 4);
+const appearanceValues = {
+	variable1: randomString(),
+	variable2: randomString(),
+	variable3: randomString(),
+};
 
 const streamOutputVariants = {
 	videoBitrate: randomNumber() * 100,
@@ -103,6 +108,11 @@ test('set offline message', async (done) => {
 	done();
 });
 
+test('set custom style values', async (done) => {
+	const res = await sendConfigChangeRequest('appearance', appearanceValues);
+	done();
+});
+
 test('verify updated config values', async (done) => {
 	const res = await request.get('/api/config');
 	expect(res.body.name).toBe(serverName);