Change CTA Submit button

I would like to change the background color and form on the “submit button” in my embedded mail chimp form.

Adding the code below to my own stylesheet does not however change anything. Any ideas ?

mc_embed_signup .button {
clear: both;
background-color: #aaa;
border: 0 none;
border-radius: 4px;
transition: all 0.23s ease-in-out 0s;
color: #FFFFFF;
cursor: pointer;
display: inline-block;
font-size: 15px;
font-weight: normal;
height: 32px;
line-height: 32px;
margin: 0 5px 10px 0;
padding: 0 22px;
text-align: center;
text-decoration: none;
vertical-align: top;
white-space: nowrap;
width: auto;
}

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