transfer.css

.container {
    width: 1000px;
    margin: 50px auto;
    border: 1px solid #ebebeb;
    border-radius: 3px;
    transition: .2s;
}

.list-group {
    display: inline-block;
    width: 400px;
    margin: 50px auto;
    vertical-align: middle;
    height: 300px;
    text-align: center;
}

.list-group-item {
    text-align: left;
}

.selected-num {
    text-align: center;
    font-size: 12px;
    margin-bottom: 10px;
}

.list-group p {
    display: inline-block;
}

.search {
    text-align: center;
}

.search .input-search {
    border: 1px solid grey;
    font-size: 12px;
    margin: 20px auto;
    width: 200px;
    padding: 5px 10px;
    border-radius: 20px;
}

.list-group input[type='search'] {
    border: none;
    outline: none;
    width: 170px;
}

.form-check-label,
.form-check-input {
    cursor: pointer;
}

.form-check-label:hover,
.form-check-input:checked+label {
    color: #409eff;
}

.transfer_button_container {
    display: inline-block;
    text-align: center;
    vertical-align: middle;
}

.transfer_button {
    width: 35px;
    height: 35px;
    border-radius: 50%;
    color: white;
    background-color: #409eff;
    border: none;
    display: block;
    margin: 20px;
    cursor: pointer;
    text-align: center;
}

.transfer_button:disabled {
    background: grey;
    cursor: not-allowed;
}

button:focus {
    outline: none;
}