SOURCE

<div class="container">
	<div class="input">
	</div>
	<div class="send">发送验证码</div>
</div>

.container {
    display: flex;
}

.input {
    width: 200px;
    height: 50px;
    border: 3px solid black;
}
.input:hover{
    border: 3px solid red;
}

.send {
    /* margin-left: -2px; */
    width: 50px;
    height: 50px;
    border-width: 3px 3px 3px 0;
    border-style: solid;
    border-color: skyblue;
}
.send:hover{
    margin-left: -2px;
    border-width: 3px 3px 3px 3px;
    border-style: solid;
    border-color: yellowgreen;
}