More default variables fallbacks

Signed-off-by: John Molakvoæ (skjnldsv) <skjnldsv@protonmail.com>

core/css/header.scss

@@ -73,7 +73,7 @@
 	/* Header menu */
 	.menu {
 		background-color: var(--color-main-background);
-		filter: drop-shadow(0 1px 10px var(--color-box-shadow));
+		filter: drop-shadow(0 1px 5px var(--color-box-shadow));
 		border-radius: 0 0 3px 3px;
 		box-sizing: border-box;
 		z-index: 2000;

core/css/variables.scss

@@ -17,16 +17,16 @@ $color-main-text: #000 !default;
 $color-main-background: #fff !default;
 
 // used for different active/disabled states
-$color-background-dark: nc-darken($color-main-background, 7%);
-$color-background-darker: nc-darken($color-main-background, 14%);
+$color-background-dark: nc-darken($color-main-background, 7%) !default;
+$color-background-darker: nc-darken($color-main-background, 14%) !default;
 
 $color-primary: #0082c9;
 $color-primary-text: #ffffff;
 // do not use nc-darken in case of overriding because
 // primary-text is independent of color-main-text
-$color-primary-text-dark: darken($color-primary-text, 7%);
-$color-primary-element: $color-primary;
-$color-primary-element-light: nc-lighten($color-primary-element, 15%);
+$color-primary-text-dark: darken($color-primary-text, 7%) !default;
+$color-primary-element: $color-primary !default;
+$color-primary-element-light: nc-lighten($color-primary-element, 15%) !default;
 
 $color-error: #e9322d;
 $color-warning: #eca700;
@@ -45,7 +45,7 @@ $image-login-background: url('../img/background.png?v=2');
 $color-loading-light: #ccc !default;
 $color-loading-dark: #777 !default;
 
-$color-box-shadow: rgba(nc-darken($color-main-background, 70%), 0.75);
+$color-box-shadow: rgba(nc-darken($color-main-background, 70%), 0.75) !default;
 
 // light border like file table or app-content list
 $color-border: nc-darken($color-main-background, 7%);