ui v2: paper component (#817)

frontend/packages/core/src/paper.tsx

+import * as React from "react";
+import styled from "@emotion/styled";
+import type { PaperProps as MuiPaperProps } from "@material-ui/core";
+import { Paper as MuiPaper } from "@material-ui/core";
+
+export interface PaperProps extends Pick<MuiPaperProps, "children"> {}
+
+const StyledPaper = styled(MuiPaper)({
+  boxShadow: "0px 4px 6px rgba(53, 72, 212, 0.2)",
+  border: "1px solid rgba(13, 16, 48, 0.1)",
+  background: "#FFFFFF",
+  padding: "16px",
+});
+
+export const Paper = ({ children }: PaperProps) => <StyledPaper>{children}</StyledPaper>;

frontend/packages/core/src/stories/paper.stories.tsx

+import * as React from "react";
+import type { Meta } from "@storybook/react";
+
+import { Paper } from "../paper";
+
+export default {
+  title: "Core/Paper",
+  component: Paper,
+} as Meta;
+
+export const Primary = () => (
+  <Paper>
+    <div>Some text in paper</div>
+  </Paper>
+);