[FIX] CSS vars usage (#27107)

...eteor/app/theme/client/imports/components/message-box.css

apps/meteor/app/theme/client/imports/general/theme_old.css

apps/meteor/app/theme/client/imports/general/variables.css

apps/meteor/app/theme/server/server.js

...ents/message/Attachments/Attachment/AttachmentDetails.tsx

.../components/message/Attachments/Files/VideoAttachment.tsx

...client/components/message/Attachments/QuoteAttachment.tsx

...client/components/message/Attachments/components/Load.tsx

...lient/components/message/Attachments/components/Retry.tsx

apps/meteor/client/head.html

apps/meteor/client/lib/clickableItem.js

apps/meteor/client/sidebar/footer/SidebarFooterDefault.tsx

.../meteor/client/views/admin/cloud/ConnectToCloudSection.js

.../views/room/MessageList/components/MessageContentBody.tsx

...eteor/ee/client/sidebar/footer/SidebarFooterWatermark.tsx

apps/meteor/package.json

ee/packages/ui-theming/.eslintrc.json

ee/packages/ui-theming/package.json

ee/packages/ui-theming/src/PaletteStyleTag.tsx

ee/packages/ui-theming/src/convertToCss.ts