fix: simplify grayscale theme

src/scss/themes/rio-grayscale.scss

@@ -1,54 +1,4 @@
-$main-theme-color: #999999;
-$body-bg-color: #4D4D4D;
-$anchor-color: #2A5858;
-$main-text-color: #000000;
-$border-color: #9EEEEE;
-$main-bg-color: #FFFFFF;
-$secondary-text-color: #444444;
-$toast-border: #9EEEEE;
-$toast-bg: #999999;
-$focus-outline: #55AAAA;
-$compose-background: lighten($main-theme-color, 32%);
-
-@import "_base.scss";
-
-$scrollbar-face: #FFFFFF !default;
-$scrollbar-face-hover: #FFFFFF !default;
-$scrollbar-face-active: #FFFFFF !default;
-$scrollbar-track: #999999 !default;
-@import "_scrollbars.scss";
-
-:root {
-
-	/* idea is navbar as rio's right-click menu */
-	--nav-bg: #E9FFE9;
-	--nav-border: #88CC88;
-	--nav-active-bg: #448844;
-	--nav-a-selected-bg: #448844;
-	--nav-a-selected-active-bg: #448844;
-	--nav-text-color: #000000;
-	--nav-text-color-hover: #FFFFFF;
-	--nav-a-bg-hover: #448844;
-	--nav-a-selected-border: #88CCCC;
-	--nav-a-border-hover: #88CCCC;
-
-	--settings-list-item-text: #{$anchor-color};
-}
-
-a, a.main-nav-link.svelte-my25xk, .settings-list-item {
-	text-decoration: underline;
-}
-a.mention.u-url, a:hover, a:active, ::selection {
-	background: #CCCCCC;
-}
-a.mention.u-url:hover, a.mention.u-url:active {
-	background: #2A5858;
-	color: #CCCCCC;
-}
-a.status-author-name, a.status-header-author {
-	text-decoration: none;
-	border-bottom: solid 1px #000000;
-}
+@import "rio.scss"
 
 img {
 	filter: grayscale(100%);