To do your own theme, you need:
1 - imagine name, for example gray
2 - define property theme with theme name.
3 - rewrite css rules with prefix fancy-theme-name,
in this sample fancy-theme-gray. 

//your-style.css

.fancy-theme-gray .fancy-field-radio-input {
    background-image: url(img/unice-radio.png);
}

.fancy-theme-gray .fancy-field-radio .fancy-field-text:hover .fancy-field-radio-input {
    background-position: 0 0px;
}

.fancy-theme-gray .fancy-field-radio-on:hover .fancy-field-radio-input {
    background-position: 0 -14px !important;
}

.fancy-theme-gray .fancy-field .fancy-field-label {
    color: #737373;
    font-family: "open sans", sans-serif;
    font-size: 14px;
    font-weight: 300;
}

.fancy-theme-gray .fancy-field-checkbox-input {
    background-image: url(img/unice-checkbox.png);
}

.fancy-theme-gray .fancy-field-checkbox-input:hover {
    background-position: 0 0px;
}

.fancy-theme-gray .fancy-checkbox-on .fancy-field-checkbox-input {
    background-position: 0 -14px;
}

.fancy-theme-gray .fancy-checkbox-on .fancy-field-checkbox-input:hover {
    background-position: 0 -14px;
}

.fancy-theme-gray .fancy-button {
    background: #168de2;
    border-radius: 20px;
    font-family: 'open sans', sans-serif;
    font-size: 14px;
    font-stretch: normal;
    font-variant: normal;
    font-weight: normal;
    padding: 0 15px;
    -webkit-transition: all 400ms ease;
    -moz-transition: all 400ms ease;
    -ms-transition: all 400ms ease;
    -o-transition: all 400ms ease;
    transition: all 400ms ease;
}

.fancy-theme-gray .fancy-button:hover {
    background-color: #ffa930;
}

.fancy-theme-gray .fancy-panel-header {
    background: #cacaca;
    background: #e2e2e2;
}

.fancy-theme-gray .fancy-panel-header .fancy-panel-header-text {
    color: #737373;
    font-family: 'open sans', sans-serif;
    font-size: 14px;
    font-weight: bold;
}

.fancy-theme-gray .fancy-field .fancy-field-text-input {
    border: 1px solid #d9d9d9;
}

.fancy-theme-gray .fancy-combo table {
    border: 1px solid #d9d9d9;
}

.fancy-theme-gray .fancy-textarea .fancy-textarea-text-input {
    border: 1px solid #d9d9d9;
}

.fancy-theme-gray.fancy-panel .fancy-panel-body {
    border: 1px solid #f2f2f2;
}

.fancy-theme-gray .fancy-form {
    background-color: #fff;
}

.fancy-theme-gray.fancy-panel .fancy-panel-bbar {
    background-color: #fff;
}

.fancy-theme-gray.fancy-combo-result-list li.fancy-combo-list-active {
    background-color: #5897fb;
}