I cannot change font-size in listbox

URCap Development HTML
1

I create the below form in installation node.
When I use the listbox, the font-size of letters cannot be changed.
They are small.

The form is written by html as below

<select id="selectNumber" style="width: 180px; height:180px; font-size:20px" size="2"></select>

図1
図1817×334 28.8 KB

2

I believe you have to change the font size of the options, not the select portion of the HTML.

.selectClass {
   font-size: 25px;
   font-family: 'Impact', cursive;
}​
<select class="selectClass">
<option value="">I'm a custom font.</option>
<option value="">Hey me too!</option>
<option value="">Averia Libre</option>
</select>
3

Thank you very much.
I tried. But I cannot solve about this.