Load proper fonts in guest.css

Fixes #4676

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

core/css/guest.css

@@ -637,3 +637,27 @@ footer,
 	height: 1px;
 	overflow: hidden;
 }
+
+/* for low-res screens, use Regular font-weight instead of Light */
+@media (-webkit-max-device-pixel-ratio: 1.3), (max-resolution: 124.8dpi) {
+	@font-face {
+		font-family: 'Open Sans';
+		font-style: normal;
+		font-weight: normal;
+		src: local('Open Sans'), local('OpenSans'), url('../fonts/OpenSans-Regular.woff') format('woff');
+	}
+}
+
+@font-face {
+	font-family: 'Open Sans';
+	font-style: normal;
+	font-weight: 300;
+	src: local('Open Sans Light'), local('OpenSans-Light'), url('../fonts/OpenSans-Light.woff') format('woff');
+}
+
+@font-face {
+	font-family: 'Open Sans';
+	font-style: normal;
+	font-weight: 600;
+	src: local('Open Sans Semibold'), local('OpenSans-Semibold'), url('../fonts/OpenSans-Semibold.woff') format('woff');
+}