JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <i>35px</i>
  <button>
    <span>default</span>
  </button>
  <button>
    <span class="middle">middle</span>
  </button>
  <button>
    <span class="bottom">bottom</span>
  </button>
  <button class="flex">
    <span>flex</span>
  </button>
</div>

CSS

* {
  box-sizing: border-box;
}
div > * {
  vertical-align: top;
}
div {
  border: 1px solid #aaa;
  background: #ffe;
}
button {
    line-height: 15px;
    padding: 10px;
    outline: none;
    border: none;
    background; #ccc;
}
.middle {
  vertical-align: middle;
}
.bottom {
  vertical-align: bottom;
}
.flex {
  display: inline-flex;
  align-items: center;
  justify-content: space-around;
}
i {
  width: 35px;
  height: 35px;
  display: inline-block;
  line-height: 35px;
  text-align: center;
  background: #cc8;
}