/* HTML is here */
<select name="work_days" id="id_work_days" multiple>
<option value="1">sun</option>
<option value="2">mon</option>
<option value="3">tue</option>
<option value="4">wed</option>
<option value="5">thu</option>
<option value="6">fri</option>
<option value="7">sat</option>
</select>
/* CSS is here */
#id_work_days{
height: 44px;
border: none;
overflow: hidden;
}
#id_work_days::-moz-focus-inner {
border: 0;
}
#id_work_days:focus {
outline: none;
}
#id_work_days option{
width: 60px;
font-size: 1.2em;
padding: 10px 0;
text-align: center;
margin-right: 20px;
display: inline-block;
cursor: pointer;
border:rgb(204, 204, 0) solid 1px;
border-radius: 5px;
color: rgb(204, 204, 0);
}