how to Centre This Input Box

I am making an app. And here I have an input box and a button. I want to center it. I tried using the center tag, it did not work. I tried using align-items:center still did not work. How to do this ??? Here is my program –

.form-inline {
  display: flex;
  flex-flow: row wrap;
  align-items: center;
}

.form-inline label {
  margin: 5px 10px 5px 0;
}

.form-inline input {
  vertical-align: middle;
  padding: 10px;
  background: transparent;
  border: 1px solid #ddd;
}

.form-inline button {
  padding: 10px 20px;
  background: transparent;
  border-right: 1px solid #ddd;
  border-top: 1px solid #ddd;
  border-bottom: 1px solid #ddd;
  color: white;
  cursor: pointer;
}

        <form class="form-inline" action="/">
          <input id="email" placeholder="Enter email" name="email" />

          <button type="submit">Submit</button>
        </form>

How to achieve this ??? Pls help

>Solution :

**justify-content: center;**

.form-inline {
    display: flex;
    flex-flow: row wrap;
    align-items: center;
    justify-content: center;
}