Adding new theme Unsplash forek from "Clouds"

Background change over each photos
Selection of "Nature" performed on Unsplash API
Kept white font for SSO main element
Remaining problems: photos color may lead to unreadable labels. Fix me!

portal/assets/themes/unsplash/custom_overlay.css

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+/*
+===============================================================================
+ This file may contain extra CSS rules loaded on all apps page (*if* the app
+ nginx's conf does include the appropriate snippet) for the small YunoHost
+ button in bottom-right corner + portal overlay.
+
+ The yunohost button corresponds to : #ynh-overlay-switch
+ The yunohost portal overlay / iframe corresponds to : #ynh-overlay
+
+ BE CAREFUL that you should *not* add too-general rules that apply to
+ non-yunohost elements (for instance all 'a' or 'p' elements...) as it will
+ likely break app's rendering
+===============================================================================
+*/
+#ynh-overlay-switch {
+  background-image: url("./cloud.png");
+}

portal/assets/themes/unsplash/custom_portal.css

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+/*
+===============================================================================
+ This file contain extra CSS rules to customize the YunoHost user portal and
+ can be used to customize app tiles, buttons, etc...
+===============================================================================
+*/
+
+/* Make page texts black */
+.user-container h2,
+.user-container small,
+.user-container .user-mail,
+.user-container .user-mail,
+.content .footer a,
+a.app-tile,
+#ynh-logout {
+  color: black !important;
+}
+
+.ynh-user-portal {
+  background-image: url('https://source.unsplash.com/random/featured/?nature') !important;
+  background-repeat: no-repeat;
+  background-size: cover;
+  width: 100%;
+  height: 100%;
+}
+
+/* Apps colors */
+.app-tile {
+  background-color: rgba(255, 255, 255, 0.5) !important;
+}
+
+.app-tile:hover:after,
+.app-tile:focus:after,
+.app-tile:hover:before,
+.app-tile:focus:before {
+    background: rgba(255, 255, 255, 0.5) !important;
+}
+
+/* Use a custom logo image */
+#ynh-logo {
+  z-index: 10;
+  background-image: url("./cloud.png");
+}
+
+/* Round the form */
+.login-form label:before {
+	border-top-left-radius: 5em ;
+	border-bottom-left-radius: 5em ;
+}
+
+.login-form * {
+	border-radius: 5em;
+}
+
+.messages {
+	border-radius: .5em;
+}

portal/assets/themes/unsplash/custom_portal.js

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+/*
+===============================================================================
+ This JS file may be used to customize the YunoHost user portal *and* also
+ will be loaded in all app pages if the app nginx's conf does include the
+ appropriate snippet.
+
+ You can monkeypatch init_portal (loading of the user portal) and
+ init_portal_button_and_overlay (loading of the button and overlay...) to do
+ custom stuff
+===============================================================================
+*/
+
+/*
+ * Monkeypatch init_portal to customize the app tile style
+ *
+init_portal_original = init_portal;
+init_portal = function()
+{
+    init_portal_original();
+    // Some stuff here
+}
+*/
+
+/*
+ * Monkey patching example to do custom stuff when loading inside an app
+ *
+init_portal_button_and_overlay_original = init_portal_button_and_overlay;
+init_portal_button_and_overlay = function()
+{
+    init_portal_button_and_overlay_original();
+    // Custom stuff to do when loading inside an app
+}
+*/