section{
background:linear-gradient(
45deg,
black 5%, yellow 0%,
yellow 10%, black 0%,
black 15%, yellow 0%,
yellow 20%, black 0%,
black 25%, yellow 0%,
yellow 30%, black 0%,
black 35%, yellow 0%,
yellow 40%, black 0%,
black 45%, yellow 0%,
yellow 50%, black 0%,
black 55%, yellow 0%,
yellow 60%, black 0%,
black 65%, yellow 0%,
yellow 70%, black 0%,
black 75%, yellow 0%,
yellow 80%, black 0%,
black 85%, yellow 0%,
yellow 90%, black 0%,
black 95%, yellow 0%,
yellow 100%, black 0%);
}
и будет как на скрине