Custom Font Not Working in WKWebView Swift

Reading the answers in the linked thread in DonMag's comment:

• Using @font-face is mandatory

• You need multiple @font-face declarations to use multiple font files as a single font family

• You need to provide baseURL to make relative urls like url(OpenSans-Regular.ttf) work

So, try this:

    let htmlString = """    <style>    @font-face    {        font-family: 'Open Sans';        font-weight: normal;        src: url(OpenSans-Regular.ttf);    }    @font-face    {        font-family: 'Open Sans';        font-weight: bold;        src: url(OpenSans-Bold.ttf);    }    @font-face    {        font-family: 'Open Sans';        font-weight: 900;        src: url(OpenSans-ExtraBold.ttf);    }    @font-face    {        font-family: 'Open Sans';        font-weight: 200;        src: url(OpenSans-Light.ttf);    }    @font-face    {        font-family: 'Open Sans';        font-weight: 500;        src: url(OpenSans-Semibold.ttf);    }    </style>    <span style="font-family: 'Open Sans'; font-weight: bold; font-size: 30; color: red">(Utils.aboutUsText)</span>    """    webView.loadHTMLString(htmlString, baseURL: Bundle.main.bundleURL) //<- 

Or you can use a separate css file if you prefer:

    let htmlString = """    <link rel="stylesheet" type="text/css" href="open-sans.css">    <span style="font-family: 'Open Sans'; font-weight: bold; font-size: 30; color: red">(Utils.aboutUsText)</span>    """    webView.loadHTMLString(htmlString, baseURL: Bundle.main.bundleURL)

open-sans.css:

@font-face{    font-family: 'Open Sans';    font-weight: normal;    src: url(OpenSans-Regular.ttf);}@font-face{    font-family: 'Open Sans';    font-weight: bold;    src: url(OpenSans-Bold.ttf);}@font-face{    font-family: 'Open Sans';    font-weight: 900;    src: url(OpenSans-ExtraBold.ttf);}@font-face{    font-family: 'Open Sans';    font-weight: 200;    src: url(OpenSans-Light.ttf);}@font-face{    font-family: 'Open Sans';    font-weight: 500;    src: url(OpenSans-Semibold.ttf);}

class StaticContentViewControlle:  WKUIDelegate, WKNavigationDelegate {    @IBOutlet weak var webViewContainer: UIView!    private var webView: WKWebView?    var url = ""        override func viewDidLoad() {        super.viewDidLoad()                initialSetup()    }        func initialSetup() {        url = "https://www.apple.com"                let myURL = URL(string: url)        if let myURL = myURL {            let myRequest = URLRequest(url: myURL)            webView?.uiDelegate = self            webView?.load(myRequest)        }        webView?.navigationDelegate = self        webView?.scrollView.showsVerticalScrollIndicator = false        webView?.scrollView.backgroundColor = .clear        webView?.isOpaque = false        webView?.backgroundColor = .clear    }                func webView(_ webView: WKWebView, didCommit navigation: WKNavigation!) {        print("Start loading")    }        func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {        print("End loading")        let textSize = 300        let javascript = "document.getElementsByTagName('body')[0].style.webkitTextSizeAdjust= '\(textSize)%'"        webView.evaluateJavaScript(javascript) { (response, error) in            print()        }    }        func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {        if navigationAction.navigationType == .linkActivated  {            if let url = navigationAction.request.url,                UIApplication.shared.canOpenURL(url) {                UIApplication.shared.open(url)                decisionHandler(.cancel)            } else {                print("Open it locally")                decisionHandler(.allow)            }        } else {            print("not a user click")            decisionHandler(.allow)        }    }}