To always show up/down arrows for input "number" with CSS, we set the opacity of the spin buttons to 1.
For instance, we write
input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
opacity: 1;
}
to select the spin buttons and set their opacity to 1 to keep the arrows showing on the number inputs.
