<form>
  <div class="fields"><label for="search">Keywords</label>
    <input type="text" id="search">
    <input type="submit" label="Search">
</form>

body {
  padding: 20px;
  font: 1em Helvetica Neue, Helvetica, Arial, sans-serif;
}

* {box-sizing: border-box;}

.fields {
  display: flex;
  align-items: center;
}

input[type="text"] {
  padding: .2em;
  font-size: 130%;
  width: 100%;
  margin: 0 0 0 1em;
}

label {
  font-size: 130%;
}

input[type="submit"] {
  border: 2px solid #333;
  padding: .2em;
  font-size: 130%;
  
}