Why does input goes outside to div when focused - HTML/CSS

Question

I have recently started a twitter clone project and have some issues with it. When I click to my input it goes a little bit down, outside the div.
My code:

      $('#searchinput').focus(function () {
            $('.middlesearchtwitter').css('background-color', 'white');
            $('.middlesearchtwitter').css('border', '1px solid rgba(29,161,242,1.00)')
        }).blur(function () {
            $('.middlesearchtwitter').css('background-color', 'rgba(0, 0, 0, 0.1)');
            $('.middlesearchtwitter').css('border', 'none')

        })

.middlehomep {
        width: 700px;
        height: 100%;
        display: inline-block;
        border-right: 1px solid lightgray;
        border-left: 1px solid lightgray;
        vertical-align: top;
    }
    .middlesearchtwitter{
        background-color: rgba(0, 0, 0, 0.1);
        border: none;
        outline: none;
        border-radius: 25px;
        width: 625px;
        height: 40px;
        margin-left: 37px;
        margin-top: 5px;
    }
    .searchicon{
        color: rgba(0, 0, 0, 0.3);
        margin-left: 15px;
        width: 50px;
        height: 50px;
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 483px;
    }
    .searchicon{
        color: rgba(0, 0, 0, 0.3);
        margin-left: 15px;
        width: 50px;
        height: 50px;
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 483px;
    }
    #searchinput:focus{
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 480px;
        background-color: white;
        border: 1px solid rgba(29,161,242,1.00);
    }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="middlehomep">
        <div class="middlesearchtwitter">
            <form action="">
                <i class="fas fa-search searchicon"></i><input id="middlesearchtwitter" type="text" placeholder="Search Twitter">
            </form>
        </div>
    </div>

I would like to do something similar to Twitter's explore page. I tried with CSS and JS, but I can't go trough this problem

Answer 1

      $('#searchinput').focus(function () {
            $('.middlesearchtwitter').css('background-color', 'white');
            $('.middlesearchtwitter').css('border', '1px solid rgba(29,161,242,1.00)')
        }).blur(function () {
            $('.middlesearchtwitter').css('background-color', 'rgba(0, 0, 0, 0.1)');
            $('.middlesearchtwitter').css('border', 'none')

        })

.middlehomep {
        width: 700px;
        height: 100%;
        display: inline-block;
        border-right: 1px solid lightgray;
        border-left: 1px solid lightgray;
        vertical-align: top;
    }
    .middlesearchtwitter{
        background-color: rgba(0, 0, 0, 0.1);
        border: none;
        outline: none;
        border-radius: 25px;
        width: 625px;
        height: 40px;
        margin-left: 37px;
        margin-top: 5px;
    }
    .searchicon{
        color: rgba(0, 0, 0, 0.3);
        margin-left: 15px;
        width: 50px;
        height: 50px;
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 483px;
    }
    .searchicon{
        color: rgba(0, 0, 0, 0.3);
        margin-left: 15px;
        width: 50px;
        height: 50px;
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 483px;
    }
#middlesearchtwitter{
padding:3px;
margin:6px;

border-radius:5px;
    #searchinput:focus{
        border-radius: 25px;
        position: absolute;
        top: 25px;
        left: 480px;
        background-color: white;
        border: 1px solid rgba(29,161,242,1.00);
    }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="middlehomep">
        <div class="middlesearchtwitter">
            <form action="">
                <i class="fas fa-search searchicon"></i><input id="middlesearchtwitter" type="text" placeholder="Search Twitter">
            </form>
        </div>
    </div>