Chore: Replace borders to `default` (#27667)

...or/app/theme/client/imports/components/contextual-bar.css

...eteor/app/theme/client/imports/components/emojiPicker.css

apps/meteor/app/theme/client/imports/components/messages.css

...eor/app/theme/client/imports/components/read-receipts.css

apps/meteor/app/theme/client/imports/components/table.css

apps/meteor/app/theme/client/imports/components/tabs.css

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

apps/meteor/app/theme/client/main.css

apps/meteor/app/theme/client/vendor/fontello/config.json

apps/meteor/app/theme/client/vendor/photoswipe.css

...ents/Omnichannel/modals/ModalSeparator/ModalSeparator.tsx

...nt/components/Omnichannel/modals/ModalSeparator/style.css

apps/meteor/client/components/Page/PageBlockWithBorder.tsx

apps/meteor/client/components/Page/PageHeader.tsx

apps/meteor/client/components/VerticalBar/VerticalBar.tsx

...eteor/client/components/VerticalBar/VerticalBarHeader.tsx

apps/meteor/client/components/message/MessageContentBody.tsx

...omponents/message/content/attachments/QuoteAttachment.tsx

...ents/message/content/attachments/file/VideoAttachment.tsx

...message/content/attachments/structure/AttachmentBlock.tsx