Edit in JSFiddle

<div class="wrap">
    <div class="inner">
        <ul>
            <li>ああああ</li>
            <li>いいいい</li>
            <li>うううう</li>
            <li>ええええ</li>
            <li>おおおお</li>
        </ul>
    </div>
</div>

* {
    box-sizing: border-box;
}

.wrap {
    position: relative;
}

.inner {
    width: 150px;
    height: 120px;
    overflow-y: scroll;

    &::before {
        content: "";
        position: absolute;
        width: 130px;
        height: 100%;
        background-color: #feffea;
        border: 1px solid #eea271;
    }

    ul {
        position: relative;
        margin: 0;
        padding: 5px;
        list-style: none;
        z-index:1;
    }

    li {
        display: flex;
        justify-content: center;
        align-items: center;
        width: 122px;
        height: 40px;
        background-color: #ccc;

        &:nth-child(n+2) {
            margin-top: 5px;
        }
    }
}