Вот правильный ответы Испытание: зигзаг [11/20]

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<polyline points="111 61.5 217.984 61.5 123.035 180.231 229.738 180.06" fill="none" stroke-width="80" stroke="teal" stroke-linecap="square" stroke-linejoin="miter"/>

<polyline points="122 61.5 217.984 61.5 123.035 180.231 218.738 180.06" fill="none" stroke-width="50" stroke="lightseagreen" stroke-linecap="round" stroke-linejoin="round"/>

<polyline points="120 61.5 217.984 61.5 123.035 180.231 220.738 180.06" fill="none" stroke="gold" stroke-width="10" stroke-linecap="miter" stroke-linejoin="bevel"/>

Код проходит, но если как учили, то не stroke-linecap=“miter”, а stroke-linecap=“butt”.