Read this:
https://www.themesandco.com/snippet/firebug-best-spent-6-minutes/
Then you will see, for example, that your “Search button” is styled something like that:
input[type="submit"] {
display: inline-block;
padding: 4px 12px;
margin-bottom: 0;
font-size: 14px;
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
line-height: 20px;
color: #333333;
text-align: center;
text-shadow: 0 1px 1px rgba(255, 255, 255, 0.75);
vertical-align: middle;
cursor: pointer;
border: 1px solid #cccccc;
border-color: #e6e6e6 #e6e6e6 #bfbfbf;
border-color: rgba(0, 0, 0, 0.1) rgba(0, 0, 0, 0.1) rgba(0, 0, 0, 0.25);
border-bottom-color: #b3b3b3;
-webkit-border-radius: 4px;
-moz-border-radius: 4px;
border-radius: 4px;
-webkit-box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.2), 0 1px 2px rgba(0, 0, 0, 0.05);
-moz-box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.2), 0 1px 2px rgba(0, 0, 0, 0.05);
box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.2), 0 1px 2px rgba(0, 0, 0, 0.05);
color: white;
text-shadow: 0 -1px 0 rgba(0, 0, 0, 0.25);
background-color: #363636;
background-image: -moz-linear-gradient(top, #444444, #222222);
background-image: -webkit-gradient(linear, 0 0, 0 100%, from(#444444), to(#222222));
background-image: -webkit-linear-gradient(top, #444444, #222222);
background-image: -o-linear-gradient(top, #444444, #222222);
background-image: linear-gradient(to bottom, #444444, #222222);
background-repeat: repeat-x;
border-color: #222222 #222222 black;
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ff444444', endColorstr='#ff222222', GradientType=0);
filter: progid:DXImageTransform.Microsoft.gradient(enabled=false);
}
You have just to create a rule in your child theme style.css or your custom css which overrides properties you want to get rid of.Something like that should work:
input[type="submit"] {
-webkit-border-radius: 0px;
border-radius: 0px;
-webkit-box-shadow: none;
box-shadow: none;
background-image: none;
background-repeat: no-repeat;
filter: none;
}