You need to adjust the viewbox as the path defined cannot be seen with the actual viewbox. Then remove the extra height definition and also remove the !important
to be able to set background-position
select {
padding: 15px;
border-radius: 3px;
height: 50px;
color: #ffffff;
padding-right: 30px;
font-size: 14px;
border-color: blue;
position: relative;
-moz-appearance: none;
-webkit-appearance: none;
appearance: none;
border: none;
background: blue url("data:image/svg+xml;utf8,<svg viewBox='0 0 140 140' width='24' height='24' xmlns='http://www.w3.org/2000/svg'><g><path d='m121.3,34.6c-1.6-1.6-4.2-1.6-5.8,0l-51,51.1-51.1-51.1c-1.6-1.6-4.2-1.6-5.8,0-1.6,1.6-1.6,4.2 0,5.8l53.9,53.9c0.8,0.8 1.8,1.2 2.9,1.2 1,0 2.1-0.4 2.9-1.2l53.9-53.9c1.7-1.6 1.7-4.2 0.1-5.8z' fill='white'/></g></svg>") no-repeat;
background-position: right 5px top 50%;
}
<select>
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="mercedes">Mercedes</option>
<option value="audi">Audi</option>
</select>
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