mdbook-admonish-custom.css

:root {
  --md-admonition-icon--admonish-exercise: url("data:image/svg+xml;charset=utf-8,<?xml version='1.0' encoding='UTF-8'?><svg xmlns='http://www.w3.org/2000/svg' id='Layer_1' data-name='Layer 1' viewBox='0 0 24 24' width='512' height='512'><path d='M2.751,15H0V14A7.634,7.634,0,0,1,4.065,7.169a10.975,10.975,0,0,1,3.9-1.09q-.889,1.1-1.783,2.338A40.582,40.582,0,0,0,2.751,15Zm12.832,2.813A40.582,40.582,0,0,1,9,21.249V24h1a7.634,7.634,0,0,0,6.831-4.065,10.975,10.975,0,0,0,1.09-3.9Q16.826,16.92,15.583,17.813ZM24,2.991c-.133,4.353-3.267,8.67-9.582,13.2A34.995,34.995,0,0,1,9,19.063V18.5A3.517,3.517,0,0,0,5.5,15H4.937A34.912,34.912,0,0,1,7.813,9.583C12.332,3.278,16.642.144,20.988,0,23.154,0,24,.885,24,2.991ZM18,8.5a2.5,2.5,0,0,0-5,0A2.5,2.5,0,0,0,18,8.5ZM1.374,23.785c1.126-.2,3.841-.758,4.748-1.664h0a3,3,0,0,0-4.243-4.243C.973,18.785.414,21.5.215,22.626l-.247,1.406Z'/></svg>");
}

:is(.admonition):is(.admonish-exercise) {
  border-color: #ffa62b;
}

:is(.admonish-exercise) > :is(.admonition-title, summary.admonition-title) {
  background-color: rgba(255, 166, 43, 0.1);
}
:is(.admonish-exercise) > :is(.admonition-title, summary.admonition-title)::before {
  background-color: #ffa62b;
  mask-image: var(--md-admonition-icon--admonish-exercise);
  -webkit-mask-image: var(--md-admonition-icon--admonish-exercise);
  mask-repeat: no-repeat;
  -webkit-mask-repeat: no-repeat;
  mask-size: contain;
  -webkit-mask-repeat: no-repeat;
}