sentry/static/app/views/monitors/components/timeline/checkInPlaceholder.tsx

import {keyframes} from '@emotion/react';
import styled from '@emotion/styled';

import {space} from 'sentry/styles/space';

const SPACING = 15;

export function CheckInPlaceholder() {
  return (
    <PlaceholderSvg xmlns="http://www.w3.org/2000/svg" width="100%" height="14px">
      <defs>
        <pattern
          id="tick-pattern"
          patternUnits="userSpaceOnUse"
          width={SPACING + 4}
          height={24}
        >
          <rect width="4px" height="14px" rx="2" fill="white" />
        </pattern>
        <mask id="pattern-mask">
          <rect width="100%" height="100%" fill="url(#tick-pattern)" />
        </mask>
      </defs>
      <foreignObject width="100%" height="14" mask="url(#pattern-mask)">
        <AnimatedGradient />
      </foreignObject>
    </PlaceholderSvg>
  );
}

const PlaceholderSvg = styled('svg')`
  margin: ${space(0.5)} 0;
`;

const gradientAnimation = keyframes`
    0%{ background-position-x: 0%; }
    100%{ background-position-x: -200%; }
`;

const AnimatedGradient = styled('div')`
  width: 100%;
  height: 100%;
  background-image: linear-gradient(
    90deg,
    ${p => p.theme.border} 0%,
    rgba(255, 255, 255, 0) 20%,
    rgba(255, 255, 255, 0) 80%,
    ${p => p.theme.border} 100%
  );
  background-size: 200% 100%;
  animation: ${gradientAnimation} 2s linear infinite;
`;