style.css

html {
    box-sizing: border-box;
    font-family: sans-serif;
}
*,
*::after,
*::before {
    box-sizing: inherit;
    margin: 0;
    padding: 0;
}

/* ----------- body element's style's */
.container {
    height: 100vh;
    background-color: #23232b;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    padding-top: 80px;
}

.dropdown-menu {
    display: grid;
    grid-template-rows: 40px max-content;
    gap: 10px;
}

.dropdown-toggle {
    all: unset;
    background-color: dodgerblue;
    color: white;
    width: 150px;
    padding: 10px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-radius: 5px;
}
.dropdown-toggle::after {
    content: " ";
    width: 6px;
    height: 6px;
    border-width: 0 2.3px 2.3px 0;
    border-style: solid;
    transform: rotate(45deg);
    transition: 0.4s;
}

.dropdown-list {
    background-color: white;
    color: #444;
    list-style: none;
    display: grid;
    grid-template-rows: repeat(4, 40px);
    border-radius: 5px;

    overflow: hidden;
    height: 0;
    transition: 0.4s;
}
.dropdown-list__item {
    display: flex;
    align-items: center;
    padding-left: 10px;
    transition: 0.4s, transform 0.4s var(--delay);
    transform: translateX(-100%);
    user-select: none;
    cursor: pointer;
}
.dropdown-list__item:hover {
    background-color: dodgerblue;
    color: #fff;
}

/* ------------- function */
.dropdown-toggle:focus::after {
    transform: rotate(225deg);
}

.dropdown-toggle:focus ~ .dropdown-list {
    height: 160px;
}
.dropdown-toggle:focus ~ .dropdown-list .dropdown-list__item {
    transform: translateX(0);
}