an example how to style buttons
The third button is an ui-template node where the icon is included as svg (From newer font-awesome versions you could download the svg-icon). If you use that you should tweak the ripple to make it feel like the ui-buttons.
[
    {
        "id": "76d2f79fde403ebf",
        "type": "tab",
        "label": "3 designed btns",
        "disabled": false,
        "info": "",
        "env": []
    },
    {
        "id": "8852173575bec666",
        "type": "ui_button",
        "z": "76d2f79fde403ebf",
        "name": "button 1",
        "group": "d921e9fe7b208126",
        "order": 1,
        "width": "2",
        "height": "2",
        "passthru": false,
        "label": "Assignment",
        "tooltip": "",
        "color": "",
        "bgcolor": "",
        "className": "styled-button",
        "icon": "mi-assignment",
        "payload": "",
        "payloadType": "str",
        "topic": "topic",
        "topicType": "msg",
        "x": 1240,
        "y": 480,
        "wires": [
            []
        ]
    },
    {
        "id": "ebdf05a4bb3726b4",
        "type": "ui_button",
        "z": "76d2f79fde403ebf",
        "name": "button 2",
        "group": "d921e9fe7b208126",
        "order": 2,
        "width": "2",
        "height": "2",
        "passthru": false,
        "label": "Basket",
        "tooltip": "",
        "color": "",
        "bgcolor": "",
        "className": "styled-button",
        "icon": "fa-shopping-basket",
        "payload": "",
        "payloadType": "str",
        "topic": "topic",
        "topicType": "msg",
        "x": 1240,
        "y": 560,
        "wires": [
            []
        ]
    },
    {
        "id": "5aa339a9467c6a4c",
        "type": "ui_template",
        "z": "76d2f79fde403ebf",
        "group": "c3bc11b854faa005",
        "name": "",
        "order": 5,
        "width": 0,
        "height": 0,
        "format": "<style>\n    .styled-button button{\n        background-color: cadetblue !important;\n        border-radius: 8px !important;\n    }\n    \n    .styled-button ui-icon{\n        display:block;\n    }\n    \n    .styled-button img{\n        width = 50px;\n        height = 50px;\n    }\n    .styled-button span{\n        font-size: 14px;\n    }\n    \n    .styled-template{\n        padding:0 !important;\n        overflow-y:unset !important;\n        vertical-align:unset !important;\n    }\n    \n    .styled-template button{\n        line-height:36px;\n    }\n</style>",
        "storeOutMessages": true,
        "fwdInMessages": true,
        "resendOnRefresh": true,
        "templateScope": "global",
        "className": "",
        "x": 1240,
        "y": 400,
        "wires": [
            []
        ]
    },
    {
        "id": "a903d8fd0deadcf8",
        "type": "ui_template",
        "z": "76d2f79fde403ebf",
        "group": "d921e9fe7b208126",
        "name": "button 3",
        "order": 3,
        "width": "2",
        "height": "2",
        "format": "<style>\n    .button-ripple{\n        overflow:hidden;\n        width:100%;\n        height:100%;\n        left:0;\n        top: 0;\n        position:absolute;\n        display:block;\n        z-index:1;\n        border-radius: inhirit;\n        background-clip: padding-box;\n        background-color: rgba(255,255,255,0);\n        transition: all 0.55s cubic-bezier(0,0,0.2,1) ;\n        -webkit-transform: translateZ(1);\n    }\n    .button-ripple:active{\n        left:50%;\n        width:0%;\n        background-color: rgba(255,255,255,0.1);\n        transition: all 0s;\n    }\n    .s36{\n        display:block;\n        vertical-align:unset;\n        width: 36px;\n        height: 36px;\n        filter:saturate(0.0) brightness(10.0) !important;\n    }\n</style>\n<button id=\"cloudbutton\" class=\"md-raised md-button\" type=\"button\" ng-click=\"OnButtonClick($event)\" aria-label=\"cloudbutton\">\n    <md-icon  class=\"s36\" md-svg-src='data:image/svg+xml;utf8,<svg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 616 512\"><path d=\"M148.6 304c8.2 68.5 67.4 115.5 146 111.3 51.2 43.3 136.8 45.8 186.4-5.6 69.2 1.1 118.5-44.6 131.5-99.5 14.8-62.5-18.2-132.5-92.1-155.1-33-88.1-131.4-101.5-186.5-85-57.3 17.3-84.3 53.2-99.3 109.7-7.8 2.7-26.5 8.9-45 24.1 11.7 0 15.2 8.9 15.2 19.5v20.4c0 10.7-8.7 19.5-19.5 19.5h-20.2c-10.7 0-19.5-6-19.5-16.7V240H98.8C95 240 88 244.3 88 251.9v40.4c0 6.4 5.3 11.8 11.7 11.8h48.9zm227.4 8c-10.7 46.3 21.7 72.4 55.3 86.8C324.1 432.6 259.7 348 296 288c-33.2 21.6-33.7 71.2-29.2 92.9-17.9-12.4-53.8-32.4-57.4-79.8-3-39.9 21.5-75.7 57-93.9C297 191.4 369.9 198.7 400 248c-14.1-48-53.8-70.1-101.8-74.8 30.9-30.7 64.4-50.3 114.2-43.7 69.8 9.3 133.2 82.8 67.7 150.5 35-16.3 48.7-54.4 47.5-76.9l10.5 19.6c11.8 22 15.2 47.6 9.4 72-9.2 39-40.6 68.8-79.7 76.5-32.1 6.3-83.1-5.1-91.8-59.2zM128 208H88.2c-8.9 0-16.2-7.3-16.2-16.2v-39.6c0-8.9 7.3-16.2 16.2-16.2H128c8.9 0 16.2 7.3 16.2 16.2v39.6c0 8.9-7.3 16.2-16.2 16.2zM10.1 168C4.5 168 0 163.5 0 157.9v-27.8c0-5.6 4.5-10.1 10.1-10.1h27.7c5.5 0 10.1 4.5 10.1 10.1v27.8c0 5.6-4.5 10.1-10.1 10.1H10.1zM168 142.7v-21.4c0-5.1 4.2-9.3 9.3-9.3h21.4c5.1 0 9.3 4.2 9.3 9.3v21.4c0 5.1-4.2 9.3-9.3 9.3h-21.4c-5.1 0-9.3-4.2-9.3-9.3zM56 235.5v25c0 6.3-5.1 11.5-11.4 11.5H19.4C13.1 272 8 266.8 8 260.5v-25c0-6.3 5.1-11.5 11.4-11.5h25.1c6.4 0 11.5 5.2 11.5 11.5z\"/></svg>'>\n    </md-icon>\n    <span>Cloud</span>\n    <div class=\"button-ripple\"></div>\n</button>\n\n<script>\n    (function(scope) {\n        scope.GetIconColor = function(){return \"white\"}\n        scope.OnButtonClick = function(evt){\n            switch(evt.currentTarget.id){\n                case \"cloudbutton\":\n                    //alert(evt.currentTarget.id);\n                    scope.send({payload: \"Cloud Button clicked\"});\n                    break;\n                default:\n                    //console.log(evt.currentTarget.id);\n                    break;\n            }\n        }\n        scope.$watch('msg', function(msg) {\n            \n        });\n    })(scope);\n</script>",
        "storeOutMessages": true,
        "fwdInMessages": true,
        "resendOnRefresh": true,
        "templateScope": "local",
        "className": "nr-dashboard-button _md styled-button styled-template",
        "x": 1240,
        "y": 640,
        "wires": [
            []
        ]
    },
    {
        "id": "d921e9fe7b208126",
        "type": "ui_group",
        "name": "Buttons",
        "tab": "d0d82445ef65a632",
        "order": 1,
        "disp": true,
        "width": "6",
        "collapse": false,
        "className": ""
    },
    {
        "id": "c3bc11b854faa005",
        "type": "ui_group",
        "name": "Channel 1",
        "tab": "",
        "order": 1,
        "disp": true,
        "width": "13",
        "collapse": false,
        "className": ""
    },
    {
        "id": "d0d82445ef65a632",
        "type": "ui_tab",
        "name": "ButtonDesign",
        "icon": "dashboard",
        "order": 3,
        "disabled": false,
        "hidden": false
    }
]