checkebox.css

*,
*::after,
*::before {
    margin: 0;
    padding: 0;
}

body {
    position: relative;
    margin: 0;
    padding: 0;
}

.body {
    position: absolute;
    top: 0;
    left: 250px;
    padding: 10px;
    height: 100vh;
    background: #ccc;
    transition: 3s;
}

.sidemenu {
    position: fixed;
    top: 0;
    left: 0;
    width: 250px;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.25);
    transition: 2s;
}

.sidemenu label {
    float: right;
    margin: 10px;
    font-size: 20px;
}

body input[type=checkbox] {
    appearance: none;
    visibility: hidden;
}

#switch:checked~.sidemenu {
    width: 50px;
}

#switch:checked~.body {
    transform: scale(1.2);
    margin: 5% auto;
    width: 70%;
}

.box {
    position: relative;
    width: 100%;
    padding: 10px;
    border-radius: 10px;
    background-color: #fff;
}

input {
    border: none;
    background: none;
    outline: none !important;
    width: 30%;
    border-radius: 10px;
    padding: 8px;
    border: 1px solid rgb(97, 97, 97);
    transition: all ease 0.9s;
}

input:focus {
    width: 100%;
}