Fix issue with dark theme

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

src/components/Composer/PreviewGridItem.vue

@@ -89,7 +89,7 @@ export default {
 }
 
 .preview-item {
-	border-radius: 4px;
+	border-radius: var(--border-radius-large);
 	background-color: #000;
 	background-position: 50%;
 	background-size: cover;

src/components/TimelinePost.vue

@@ -44,7 +44,7 @@
 				v-tooltip="t('social', 'Boost')"
 				@click="boost">
 				<template #icon>
-					<Repeat :size="20" :fill-color="isBoosted ? 'blue' : 'black'" />
+					<Repeat :size="20" :fill-color="isBoosted ? 'blue' : 'var(--color-main-text)'" />
 				</template>
 			</NcButton>
 			<NcButton v-if="!isLiked"