<ul class="group">
  <li>
    <input class="form-control" type="text" value="Input element">
  </li>
  
  <li>
    <button class="btn">Button</button>
  </li>
</ul>

<ul class="group group--xl">
  <li>
    <input class="form-control" type="text" value="Input element XL">
  </li>
  
  <li>
    <button class="btn">Button XL</button>
  </li>
</ul>

<ul class="group">
  <li>
    <button class="btn">
      <svg class="icon margin-right" viewBox="0 0 16 16" aria-hidden="true"><path d="M8,0a8,8,0,1,0,8,8A8,8,0,0,0,8,0Zm2.629,11.618L8,10.236,5.371,11.618l.5-2.927L3.747,6.618l2.939-.427L8,3.528,9.314,6.191l2.939.427L10.127,8.691Z"></path></svg>
      <span>Button</span>
    </button>
  </li>
</ul>
.btn, .form-control {
  // reset
  background-color: transparent;
  padding: 0;
  border: 0;
  border-radius: 0;
  color: inherit;
  appearance: none;
  
  // make sure properties affecting height have same value
  font-size: 1em;
  line-height: 1.2;
  padding: 0.5em var(--padding-x);
  border-width: 2px;
  border-style: solid;
}

// button
.btn {
  display: inline-flex;
  justify-content: center;
  align-items: center;
  
  background-color: hsl(220, 90%, 56%);
  --padding-x: 1.2em;
  border-color: transparent;
  border-radius: 0.25em;
  box-shadow: 0 1px 4px hsla(220, 90%, 37%, 0.25);
  
  color: white;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  
  transition: .2s;
  
  &:hover {
    background-color: hsl(220, 90%, 50%);
  }

  &:focus {
    outline: none;
    box-shadow: 0px 0px 0px 2px hsla(220, 90%, 56%, 0.2);
  }
  
  &:active {
    transform: translateY(2px);
  }
}

// input
.form-control {
  background-color: white;
  --padding-x: 0.5em;
  border-color: hsl(240, 1%, 83%);
  border-radius: 0.25em;
  
  color: hsl(240, 4%, 20%);
  
  transition: .2s;
  
  &:hover {
    border-color: hsl(240, 1%, 72%);
  }
  
  &:focus {
    outline: none;
    border-color: hsl(220, 90%, 56%);
    box-shadow: 0 0 0 2px hsla(220, 90%, 56%, 0.2);
  }
}

// icon
.icon {
  display: inline-block;
  color: inherit;
  fill: currentColor;
  height: 1em;
  width: 1em;
  line-height: 1;
  flex-shrink: 0;
  max-width: initial;
}

// utility classes
.margin-right {
  margin-right: 0.25rem;
}

// demo
*, *::after, *::before {
  box-sizing: inherit;
}

* {
  font: inherit;
}

html {
  box-sizing: border-box;
}

body {
  padding: 2em;
  font-family: system-ui;
}

.group {
  --gap: 0.5rem;
  display: flex;
  flex-wrap: wrap;
  margin-left: calc(-1 * var(--gap));
  margin-bottom: calc(-1 * var(--gap));
  padding-bottom: 1rem;
  
  > * {
    margin-left: var(--gap);
    margin-bottom: var(--gap);
  }
}

.group--xl {
  font-size: 1.25em;
}
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