index.css

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

.main {
    padding: 40px;
}

.my-select {
    display: inline-block;
    width: auto;
    min-width: 80px;
    box-sizing: border-box;
    vertical-align: middle;
    color: #515a6e;
    font-size: 14px;
    line-height: normal;
    position: relative;
}

.select-selection {
    display: block;
    box-sizing: border-box;
    outline: 0;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    cursor: pointer;
    position: relative;
    background-color: #fff;
    border-radius: 4px;
    border: 1px solid #dcdee2;
    transition: all .2s ease-in-out;
}

.select-selection:hover,
.select-selection.select-focus {
    border-color: #57a3f3;
    box-shadow: 0 0 0 2px rgba(45, 140, 240, .2);
}

.select-selected-value {
    display: block;
    height: 28px;
    line-height: 28px;
    font-size: 12px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    padding-left: 8px;
    padding-right: 24px;
}

.icon-select-arrow {
    position: absolute;
    top: 50%;
    right: 8px;
    line-height: 1;
    margin-top: -7px;
    font-size: 14px;
    color: #808695;
    transition: all .2s ease-in-out;
    display: inline-block;
    font-style: normal;
    font-weight: 400;
    font-variant: normal;
    text-transform: none;
    text-rendering: auto;
    line-height: 1;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    vertical-align: middle;
}

.icon-select-arrow::before {
    content: "";
    display: block;
    width: 6px;
    height: 6px;
    background-color: transparent;
    border-left: 1.5px solid #808695;
    border-bottom: 1.5px solid #808695;
    transform: rotate(-45deg);
}

.select-dropdown {
    width: auto;
    min-width: 80px;
    max-height: 200px;
    overflow: auto;
    margin: 5px 0;
    padding: 5px 0;
    background-color: #fff;
    box-sizing: border-box;
    border-radius: 4px;
    box-shadow: 0 1px 6px rgba(0, 0, 0, .2);
    position: absolute;
    z-index: 2;
    transform-origin: center top 0px;
    transition: all 0.3s;
    will-change: top, left;
    top: 30px;
    left: 0;
    transform: scale(1, 0);
    opacity: 0;
}

.select-item {
    line-height: normal;
    padding: 7px 16px;
    clear: both;
    color: #515a6e;
    font-size: 12px !important;
    white-space: nowrap;
    list-style: none;
    cursor: pointer;
    transition: background .2s ease-in-out;
}

.select-item.select-item-selected,
.select-item:hover {
    color: #2d8cf0;
    background-color: #f3f3f3;
}