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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

     

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

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About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient. For instance, CoffeeScript can help prevent easy-to-make mistakes and offer a cleaner syntax and Babel can bring ECMAScript 6 features to browsers that only support ECMAScript 5.

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You're using npm packages, so we've auto-selected Babel for you here, which we require to process imports and make it all work. If you need to use a different JavaScript preprocessor, remove the packages in the npm tab.

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Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

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About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

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HTML

            
              <svg xmlns="http://www.w3.org/2000/svg" width="0" height="0" viewBox="0 0 100 100">
        <defs>
            <linearGradient id="gradient" x1="0%" y1="0%" x2="100%" y2="0%">
                <stop offset="0%" stop-color="#00bc9b" />
                <stop offset="100%" stop-color="#5eaefd" />
            </linearGradient>
            <linearGradient id="gradient2" x1="0%" y1="0%" x2="100%" y2="0%">
                <stop offset="0%" stop-color="#5eaefd" />
                <stop offset="100%" stop-color="#00bc9b" />
            </linearGradient>
        </defs>
    </svg>
    <div class="group">
        <ul class="c-nav underliner">
            <li class="c-nav__item"><a href="#">News & Politics</a></li>
            <li class="c-nav__item"><a href="#">Culture</a></li>
            <li class="c-nav__item"><a href="#">Technology</a></li>
            <li class="c-nav__item"><a href="#">Business</a></li>
            <li class="c-nav__item"><a href="#">Human Interest</a></li>
        </ul>
        <ul class="c-nav c-nav-2 underliner-small">
            <li class="c-nav__item"><a href="#">Works</a></li>
            <li class="c-nav__item"><a href="#">Articles</a></li>
            <li class="c-nav__item"><a href="#">About</a></li>
            <li class="c-nav__item"><a href="#">Contact Me</a></li>
            <li class="c-nav__item"><a href="#">My Books</a></li>
        </ul>
    </div>


<hr>

<p class="ishadeed">Read the article on <a href="https://ishadeed.com/article/custom-underline-svg/">ishadeed.com</a>. <a href="https://github.com/shadeed/underliner">Github</a></p>
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CSS

            
              body {
	padding: 1rem;
	font-family: 'IBM Plex Sans', sans-serif;
}

svg {
	display: block;
}

.group {
	//outline: 1px solid lightgrey;
	padding: 1rem;
	margin-bottom: 2.5rem;
}

.c-nav {
  &:not(:last-child) {
    margin: 1rem 0 2rem;
  }

	@media (min-width: 900px) {
		display: flex;
		justify-content: center;
	}
}

.c-nav__item {
	margin-right: 1.5rem;
	font-size: 1.5rem;

	a {
		display: inline-block;
		text-decoration: none;
		color: #000;
		margin-bottom: 4px;
		transition: 0.4s;
	}

	svg {
		pointer-events: none;
        transition: 0.5s;
        //outline: solid 1px lightgrey;
	}

	path {
        transition: stroke-dasharray 0.5s, stroke-dashoffset 0.5s, opacity 0.5s;
        
        &:last-child {
            opacity: 0.2;
        }
	}

	a {
		&:hover,
		&:focus {
			color: #00bc9b;
		}
	}

	a:hover + svg,
	a:focus + svg {
		opacity: 1;

		path {
			stroke-dashoffset: 0;	
		}
	}
}

#path1 {
	opacity: 0.25;
}

.c-form {
	max-width: 500px;
	margin: 0 auto;

	legend {
		margin-bottom: 1rem;
		font-weight: bold;
	}

	label {
		user-select: none;
	}
}

.c-form__item {
	margin-bottom: 1rem;
}

.c-nav-2 {
	.c-nav__item {
		font-size: 1rem;
	}
}

hr {
  border: 0;
  height: 1px;
  background: lightgrey;
}

.ishadeed {
  text-align: center;
  
  a {
    color: #3563D9;
  }
}
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JS

            
              class Underliner {
    constructor(selector, color1, color2, thickness1, thickness2, strokeLinecap, rtl) {
        this.links = document.querySelectorAll(selector)
        this.fill = 'transparent';
        this.color1 = color1;
        this.color2 = color2;
        this.thickness1 = thickness1;
        this.thickness2 = thickness2;
        this.strokeLinecap = strokeLinecap;
        this.rtl = rtl;
        this.init();
    }

    init() {
        let self = this;

        self.links.forEach(function (link) {
            let linkWidth = parseInt(link.offsetWidth);
            let svg = self.createSVG(linkWidth);
            self.insertAfter(svg, link);
        });
    }

    setPath(pathD, color, thickness, strokeLinecap) {
        const path = document.createElementNS("http://www.w3.org/2000/svg", "path");

        path.setAttribute("d", pathD);
        path.setAttribute("fill", this.fill);
        path.setAttribute("stroke", color);
        path.setAttribute("stroke-width", thickness);
        path.setAttribute("stroke-linecap", strokeLinecap);
        path.setAttribute("stroke-dasharray", path.getTotalLength() + 10);
        path.setAttribute("stroke-dashoffset", path.getTotalLength() + 10);

        return path;
    }

    randomizePath(linkWidth) {
        let moveYMin = 5;
        let moveYMax = 12;

        let curveXMin = 15;
        let curveXMax = linkWidth; /* Width of the link */
        let curveYMin = 7;
        let curveYMax = linkWidth * 0.12; /* Making the quadratic propotional to the link width */
        //let curveYMax = 20

        let endYMin = 5;
        let endYMax = 11;

        let moveY = Math.floor(Math.random() * (moveYMax - moveYMin)) + moveYMin;
        let curveX = Math.floor(Math.random() * (curveXMax - curveXMin)) + curveXMin;
        let curveY = Math.floor(Math.random() * (curveYMax - curveYMin)) + curveYMin;
        let endY = Math.floor(Math.random() * (endYMax - endYMin)) + endYMin;

        return `M5 ${moveY} Q ${curveX} ${curveY} ${linkWidth - 7} ${endY}`
    }

    createSVG(linkWidth) {
        const svg = document.createElementNS("http://www.w3.org/2000/svg", "svg");

        svg.setAttribute("width", linkWidth);
        svg.setAttribute("height", "35");

        const path = document.createElementNS("http://www.w3.org/2000/svg", "path");
        const path2 = document.createElementNS("http://www.w3.org/2000/svg", "path");

        let pathD = this.randomizePath(linkWidth);
        let pathD2 = this.randomizePath(linkWidth);

        if(this.rtl === true) {
            pathD = this.reverseMe(pathD);
            pathD2 = this.reverseMe(pathD2);
        }

        svg.appendChild(this.setPath(pathD, this.color1, this.thickness1, this.strokeLinecap));
        svg.appendChild(this.setPath(pathD2, this.color2, this.thickness2, this.strokeLinecap));

        svg.setAttribute("focusable", false);

        return svg;
    }

    reverseMe(path) {
        /* Regex functions borrwed from 
        https://github.com/krispo/svg-path-utils/blob/master/src/svg-path-utils.js */
        let pathOperators = path.replace(/[\d,\-\s]+/g, '').split('');
        let pathNums = path.replace(/[A-Za-z,]+/g, ' ').trim().replace(/\s\s+/g, ' ').split(' ');
    
        return `${pathOperators[0]} ${pathNums[4]} ${pathNums[5]} ${pathOperators[1]} ${pathNums[2]} ${pathNums[3]} ${pathNums[0]} ${pathNums[1]}`;
    }

    // https://plainjs.com/javascript/manipulation/insert-an-element-after-or-before-another-32/
    insertAfter(el, referenceNode) {
        referenceNode.parentNode.insertBefore(el, referenceNode.nextSibling);
    }
}

let test = new Underliner(".underliner a", "url(#gradient)", "url(#gradient2)", 7, 12, "round", false);

let test2 = new Underliner(".underliner-small a", "url(#gradient)", "url(#gradient2)", 3, 6, "round");
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