Change the style of the product-variant (combobox) in the product block

I can only do the above design in the chrome inspector with this code:

element.style {
 text-transform: none;
 height: 35;
 width: 185;
 margin: auto;
 border: 1 solid #d5d5d5;
 border-radius: 0.4;
 background-color: #209D50;
 color: white;
 text-align: center;
}

#block-yui_3_17_2_1_1635989652851_13463 .variant-option .variant-select-wrapper .select {
    text-transform: none;
    height: 35px;
    width: 185px;
    margin: auto;
    border: 1px solid #d5d5d5;
    border-radius: 0.4em;
    background-color: #209D50;
    color: white;
    text-align: center;
}