<div class="form-group">
  <input type="text" class="form-control" id="inputText">
  <button type="button" class="btn btn-primary">按钮</button>
</div>

.form-group {
  display: flex;
  align-items: center;
}

.form-control {
  margin-right: 10px;
}

.form-group {
  overflow: hidden;
}

.form-control {
  float: left;
  margin-right: 10px;
}

var button = document.querySelector('.btn');
button.addEventListener('click', function() {
  // 处理按钮点击事件
});