When creating a web page and there is are issues with the layout it can in many cases difficult to figure out.

Add the following to your project debugger.css

* {
    outline: 1px solid red;
}

    *:hover {
        outline: 2px solid blue;
    }

Add a link to the page needing attention e.g.

<link rel="stylesheet" href="css/debugger.css" />

Render the page and we get something like this.

For ASP.NET we can conditionally add the style sheet in _Layout.cshtml

<environment names="development">
    <link rel="stylesheet" href="css/debugger.css"/>
</environment>

Even better

Rather than adding/removing debugger.css manually this can be done with JavaScript.

Add the following JavaScript file, in this case under lib/css

var $debugHelper = $debugHelper || {};
$debugHelper = function () {

    /*
     * Add/remove debugger.css to the current page
     */

    var href = "lib/debugger.css";
    var addCss = function () {
        if (isCssLoaded(href) === true) {
            return;
        }
        var head = document.head;
        var link = document.createElement("link");

        link.type = "text/css";
        link.rel = "stylesheet";
        link.href = href;

        head.appendChild(link);
    };

    var removeCss = function () {

        if (isCssLoaded('debugger.css')) {
            document.querySelector(`link[href$="${href}"]`).remove();
        }

    };

    var toggle = function() {
        if (isCssLoaded(href) === true) {
            removeCss();
        } else {
            addCss();
        }
    }

    var isCssLoaded = function () {

        for (var index = 0, count = document.styleSheets.length; index < count; index++) {
            var sheet = document.styleSheets[index];

            if (!sheet.href) {
                continue;
            }

            if (sheet.href.includes(href)) {
                return true;
            }

        }

        return false;
    }

    return {
        addCss: addCss,
        removeCss: removeCss,
        isCSSLinkLoaded: isCssLoaded,
        toggle: toggle
    };
}();

In a HTML file reference the file above.

<script src="lib/debugHelper.js"></script>

In the same file add a script section with the following code. Show the page, press ALT + 1 to add/remove the stylesheet file.

<script>

    /* 
     * Karen code
     * ALT+1 toggles adding/removing debugger.css
     */
    document.addEventListener('keydown', function (event) {

        if (event.key === '1' && event.altKey) {
            $debugHelper.toggle();
        }

    });

</script>

Source code

See the following GitHub Gist.

Basic CSS debugging tip

Even better

Source code

See also