實現程式碼：

css樣式：利用flex佈局實現

body{
    display: flex;
    justify-content: space-around;
}
#wrap{
    width: 200px;
    height: 200px;
    background: #F0F0F0;
}
header{
    height:28px;
    line-height:28px;
    background: #2e353d;
    color: white;
    font-size: 16px;
    text-align: center;
}
header+#content
 
{
    box-sizing: border-box;
    margin-top: 10px;
}
#content{
    padding: 10px;
}
input,button{
    width: 100%;
}
input[type="text"],input[type="password"]{
    height: 35px;
    margin-top: 10px;
}
button{
    height: 30px;
    margin-top: 20px;
}