index.html

<style>
  p.hint.tip,
  p.hint.error,
  p.hint.warn {
    letter-spacing: 0;
    box-sizing: border-box;
    font-size: inherit;
    line-height: 1.6rem;
    word-spacing: 0.05rem;
    background-color: rgba(238, 238, 238, 0.5);
    border-bottom-right-radius: 2px;
    border-top-right-radius: 2px;
    padding: 8px 12px 8px 24px;
    margin-bottom: 16px;
    position: relative;
  }

  p.hint.tip:before,
  p.hint.error:before,
  p.hint.warn:before {
    border-radius: 100%;
    color: #fff;
    content: '!';
    font-size: 14px;
    font-weight: 700;
    left: -12px;
    line-height: 20px;
    position: absolute;
    height: 20px;
    width: 20px;
    text-align: center;
    top: 12px;
  }

  p.hint.tip {
    border-left: 4px solid #27ab83;
  }

  p.hint.tip:before {
    background-color: #27ab83;
  }

  p.hint.warn {
    border-left: 4px solid #f0b429;
  }

  p.hint.warn:before {
    background-color: #f0b429;
  }

  p.hint.error {
    border-left: 4px solid #ef4e4e;
  }

  p.hint.error:before {
    background-color: #ef4e4e;
  }
</style>
<p class="hint tip">
  You can check out the full source code of this example
  <a href="https://github.com/sergioramos/remark-hint">here</a>.
</p>
<p class="hint warn">
  You can check out the full source code of this example
  <a href="https://github.com/sergioramos/remark-hint">here</a>.
</p>
<p class="hint error">
  You can check out the full source code of this example
  <a href="https://github.com/sergioramos/remark-hint">here</a>.
</p>