style.css

body {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    justify-content: flex-start;
    margin: 0;
}

.controls {
    display: flex;
    flex-direction: row;
    align-items: center;
    width: 100%
}

label {
    white-space: nowrap;
}

button {
    height: 25px;
    background-color: #4CAF50;
    color: #fff;
    border: none;
    outline: none;
    opacity: 0.7;
    -webkit-transition: .2s;
    transition: opacity .2s;
    cursor: pointer;
}

input, button {
    margin: 10px;
}

button:hover {
    opacity: 1;
}

input[type='range'] {
    -webkit-appearance: none;
    width: 100%;
    height: 25px;
    background: #d3d3d3;
    outline: none;
    opacity: 0.7;
    -webkit-transition: .2s;
    transition: opacity .2s;
}

input[type='range']:hover {
    opacity: 1;
}

input[type='range']::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 25px;
    height: 25px;
    background: #4CAF50;
    cursor: pointer;
}

input[type='range']::-moz-range-thumb {
    width: 25px;
    height: 25px;
    background: #4CAF50;
    cursor: pointer;
}