如何使这个输入框居中

how to Centre This Input Box

我正在制作一个应用程序。在这里我有一个输入框和一个按钮。我想把它居中。我尝试使用 center 标签,但没有用。我尝试使用 align-items:center 仍然没有用。这该怎么做 ???这是我的程序 -



.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>

如何实现???请帮忙

.formContainer {
  display: block;
  text-align: center;
}

.form-inline {
  display: inline-flex;
  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;
}
<div class="formContainer">
  <form class="form-inline" action="/">
    <input id="email" placeholder="Enter email" name="email" />
    <button type="submit">Submit</button>
  </form>
</div>

**justify-content: center;**

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

form {
  display: flex;
  justify-content: center;
  align-items: center;
  
  /* Use this line if you have to add multiple elements */
  flex-direction: column;
}
<form class="form-inline" action="/">
  <div class="input-field">
    <input id="email" placeholder="Enter email" name="email" />
    <button type="submit">Submit</button>
  </div>
</form>

使用 justify-content: center; 使其居中对齐

.form-inline {
  display: flex;
  justify-content: center;
  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: black;
  cursor: pointer;
}
<form class="form-inline" action="/">
          <input id="email" placeholder="Enter email" name="email" />

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