.battery {
    position: relative;
    width: 300px;
    height: 100px;
    border: 3px solid black;
    margin-bottom: 10px;
}

.battery::before {
    content: "";
    display: block;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: green;
    width: calc(var(--level, 100%));
}

.battery[data-level="25"]::before {
    --level: 25%;
    background-color: red;
}

.battery[data-level="50"]::before {
    --level: 50%;
    background-color: yellow;
}

.battery::after {
    content: "";
    display: block;
    position: absolute;
    height: 35px;
    top: 32px;
    right: -12px;
    /* bottom: 5px; */
    width: 2px;
    border-right: 10px solid black;
}