<select>
<option value="option1">選項1</option>
<option value="option2">選項2</option>
<option value="option3">選項3</option>
</select>

select {
width: 150px;
border: 1px solid #ccc;
background-color: #fff;
padding: 5px;
}

option {
font-size: 14px;
color: #333;
background-color: #fff;
}

select:focus {
outline: none;
}
select:not(:focus) option:first-child {
display: none;
}
select:not(:focus) option {
display: block;
}