Thanks Dmytro Rutkovskyi, I'll try the above approach and attach the CSS file to the Knowledge Article page and see if it works. Once it works I'll mark this question as resolved!
EDIT: So I've included the CSS to the Knowledge article (see screenshot below) from the portal front end:
@import url(https://fonts.googleapis.com/css?family=Open+Sans:400,300,300italic,400italic,600,600italic,700italic,700);.hiq-t{margin:0;padding:0}.hiq-t div,.hiq-t dl,.hiq-t dt,.hiq-t dd,.hiq-t ul,.hiq-t ol,.hiq-t li,.hiq-t h1,.hiq-t h2,.hiq-t h3,.hiq-t h4,.hiq-t h5,.hiq-t h6,.hiq-t pre,.hiq-t form,.hiq-t fieldset,.hiq-t input,.hiq-t p,.hiq-t blockquote,.hiq-t th,.hiq-t td{margin:0;padding:0;}.hiq-t ,.hiq-t {border:0}.hiq-t img{border:0}.hiq-t address,.hiq-t caption,.hiq-t cite,.hiq-t code,.hiq-t dfn,.hiq-t em,.hiq-t th,.hiq-t var{font-style:normal;font-weight:normal;}.hiq-t b,.hiq-t strong{font-weight:bold;font-style:inherit}.hiq-t ol,.hiq-t ul{list-style:none;}.hiq-t caption,.hiq-t th{text-align:left;}.hiq-t h1,.hiq-t h2,.hiq-t h3,.hiq-t h4,.hiq-t h5,.hiq-t h6{font-size:100%;}.hiq-t q:before,.hiq-t q:after{content:'';}.hiq-t em{font-weight: inherit;font-style: italic;}.hiq-t{background-color:#FFF;color:#262626;font-family:'Open Sans',sans-serif;font-size: 14px;padding:15px;margin: 0px;margin-right: 0px;margin-bottom: 20px;font-weight: normal;}.hiq-t HR{border: 0;color: #E4E4E4;background-color: #E4E4E4;height: 1px;width: 100%;text-align: left;overflow:hidden;margin: 0;margin-top:15px;margin-bottom: 5px; }.hiq-t img{border: 0px;}.hiq-t em{font-style: italic;}.hiq-t .computer_code{background-color:#f9f9f9;font-family:"Consolas", "Courier New", Courier, mono, serif;font-size:12px;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;line-height: 1.7em;color:#666;padding:5px;border:1px solid #999 }.hiq-t .tip{color: #c09853;background-color: #fcf8e3;padding: 8px 35px 8px 25px;margin-bottom: 20px;text-shadow: 0 1px 0 rgba(255, 255, 255, 0.5);border: 1px solid #fbeed5;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;}.hiq-t .info{color: #3a87ad;background-color: #d9edf7;padding: 8px 35px 8px 25px;margin-bottom: 20px;text-shadow: 0 1px 0 rgba(255, 255, 255, 0.5);border: 1px solid #bce8f1;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;}.hiq-t .warning{background: #F5E5DA url(/images/warning.png) 5px 50% no-repeat;padding: 8px 35px 8px 25px;margin-bottom: 20px;text-shadow: 0 1px 0 rgba(255, 255, 255, 0.5);border: 1px solid #FFB7A9;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;color: #CC3300;}.hiq-t .clearfloat{clear:both;height:0;font-size: 1px;line-height: 0px; }.hiq-t tt,.hiq-t kbd{font-family:"Consolas", "Courier New", Courier, mono, serif;font-size:12px;}.hiq-t a{color: #00BD9D;cursor: pointer;}.hiq-t a:link{color: #00BD9D;text-decoration:none}.hiq-t a:hover{color: #555;text-decoration: none}.hiq-t p{line-height: 1.6em }.hiq-t p{margin:0;padding:0 }.hiq-t H1{font-family:'Open Sans', sans-serif;color: #00bd9d;font-size: 2.75em;font-weight: 400;line-height: 60px;margin-bottom: 25px;}.hiq-t H2{font-family:'Open Sans', sans-serif;font-size: 2.2em;font-weight: 300;line-height: 40px;margin-bottom: 15px;}.hiq-t H3{font-family:'Open Sans', sans-serif;font-size: 1.6em;font-weight: 300;line-height: 30px;margin-bottom: 15px;}.hiq-t H4{font-family:'Open Sans', sans-serif;font-size: 1.5em;font-weight: 400;margin-bottom: 15px;}.hiq-t H5{font-family:'Open Sans', sans-serif;font-size: 1.125em;font-weight: 400;margin-bottom: 15px;}.hiq-t ul{list-style-type:disc;margin: 5px 0 0 9px;padding: 0 0 0 12px;}.hiq-t li{margin-bottom: 7px;line-height:160%;}.hiq-t ol{list-style-type:decimal;margin:0 0 10px 30px;line-height:180%;}.hiq-t ol li{margin-bottom: 6px;}.hiq-t table{border-collapse:collapse;border-spacing:0;width: 75%;font-family:'Open Sans', sans-serif;}.hiq-t table tr td{border-right:1px solid #CCC;border-left:1px dotted #CCC;border-top:1px solid #CCC;border-bottom:1px solid #CCC;padding: 8px;vertical-align:top;}.hiq-t table th{background-color: #00bd9d;color: white;margin-bottom: 0;border:1px solid #ccc;padding: 8px;text-align:left;}.hiq-t table td{font-family: inherit;}.hiq-t table tr:nth-child(odd){background-color:#ffffff;}.hiq-t table tr:nth-child(even){background-color:#f9f9f9;}.hiq-t table tr:hover{background-color: #ddd;}.hiq-t .left{text-align:inherit}.hiq-t .center{text-align:center }.hiq-t .right{text-align:right }.hiq-t .full{text-align:justify }.hiq-t img.left,.hiq-t table.left{float:left;text-align:inherit}.hiq-t img.center,.hiq-t table.center{margin-left:auto;margin-right:auto;text-align:inherit}.hiq-t img.center{display:block}.hiq-t img.right,.hiq-t table.right{float:right;text-align:inherit}.hiq-t .intro{width:800px;padding-bottom:25px}.hiq-t .container{overflow: hidden;width: 850px;}.hiq-t .container .columns{border:#cccccc 1px solid;float: left;margin: 0 15px 0 0;text-align: left;width: 600px;overflow:hidden;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;box-shadow: 0 1px 2px 1px #e9eded;}.hiq-t .container .contact{background: #ffffff;border: 1px solid #D8DEE3;float: left;margin: 0;padding: 10px;text-align: left;width: 200px;-webkit-border-radius: 4px;-moz-border-radius: 4px;border-radius: 4px;box-shadow: 0 1px 2px 1px #e9eded;}.hiq-t .container .contact h2{color: #333333;font-family:'Open Sans', sans-serif;font-size: 14px;font-weight: bold;margin: 0 0 7px;}.hiq-t .columns .header{background-color: #f2f2f2;color: #666;font-size: 14px;font-weight: 300;padding: 8px 17px 8px 10px;text-align: left;clear:both}.hiq-t .columns .col-inner{color: #333333;padding: 12px 5px 5px;}.hiq-t .columns .left-col{width:50%;float:left}.hiq-t .columns .right-col{width:50%;float:right}@media only screen and (min-device-width : 320px) and (max-device-width : 1024px){.hiq-t .intro,.hiq-t .container{width:100%}.hiq-t .container .columns{float:none;margin:0 5px 5px 0;background:none;width:100%}.hiq-t .container div.contact{float:none;margin-top: 20px;width:100%;}}@media only screen and (min-device-width : 320px) and (max-device-width : 480px){.hiq-t .columns .left-col,.hiq-t .columns .right-col{float:none;width:auto}} .hiq-t #searchContainer{font-size:12px;margin-bottom:20px;margin-left:0;margin-top:0;padding:10px 5px 10px 20px;max-width:800px;background: #F2F2F2;clear: left;min-width: 600px;white-space: nowrap;-webkit-border-radius: 2px;-moz-border-radius: 2px;border-radius: 2px;}.hiq-t h2.morehelp{font-size:14px;font-weight:bold;margin:0px 0 7px;font-family:'Open Sans', sans-serif;color:#333}.hiq-t h2.search{font-size:28px;font-weight:300;margin:0px 0 9px;overflow:hidden;font-family:'Open Sans', sans-serif;color:#333}.hiq-t .searchInput{margin:0px;padding-left:10px;padding-right:15px;padding-top:8px;padding-bottom:7px;border-left:#ccc 1px solid;border-top:#ccc 1px solid;border-right:#ccc 1px solid;border-bottom:#ccc 1px solid;width:520px;background:url("/images/kbsearch_bg.gif") #fff repeat-x center top;color:#333;font-size:15px;vertical-align:text-top}.hiq-t .searchInput:focus{box-shadow: 0 0 5px rgba(82,168,236,.5);-webkit-box-shadow: 0 0 5px rgba(82,168,236,.5);-moz-box-shadow: 0 0 5px rgba(82,168,236,.5);border: 1px solid rgba(82,168,236,.75);}.hiq-t .searchButton{-moz-border-radius:5px 5px 5px 5px;background:url("/images/button-bg.gif") repeat-x scroll left bottom #FEFFFE;border-color:#DDD #CCC #CCC #DDD;border-style:solid;border-width:1px;color:#555;cursor:pointer;font-family:Arial, "Lucida Grande";margin:0;font-size:20px;margin:0 0 0 5px;padding:5px 10px 5px;vertical-align:text-top}.hiq-t .searchButton:active,.hiq-t .searchButton.active{background-position:left top}.hiq-t .searchButton:hover,.hiq-t .searchButton.hover{border-color:#069;color:#069}.hiq-t table td#header_left,.hiq-t table td#header_right{border-bottom:1px solid #ccc;border-right:0px;border-left:0px;border-top:0px;padding:2px;}.hiq-t table td#footer_left,.hiq-t table td#footer_right{border-top:1px solid #ccc;border-right:0px;border-left:0px;border-bottom:0px;padding:2px;}.hiq-t iframe:focus{outline: none;}.hiq-t iframe[seamless]{display: block;}