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CSS

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HTML 

              
                <div id="root"></div>
!

CSS 

              
                $light: #fff;
$dark: #222;
$blue: #2196f3;
$red: #fb3838;

body {
	box-sizing: border-box;
	height: 100%;
}

/* Form
----------------------------*/
form {
	overflow: hidden;
	width: 300px;
	margin: 1em auto;
	select,
	input {
		font-weight: 500;
		font-size: 1em;
		line-height: 1em;
		width: calc(100% / 3 - 0.4em);
		height: 2.5em;
		float: left;
		padding: 0.5em;
		margin: 0 0.2em;
		border: 1px solid lighten($dark, 80%);
		border-width: 0 0 2px 0;
		background: transparent;
		color: $dark;
		outline: none;
		transition: all 500ms ease-in-out;
		&:hover,
		&:focus {
			cursor: pointer;
			outline: none;
			transition: all 500ms ease-in-out;
		}
	}
	input[type="submit"] {
		border: 1px solid $blue;
		background: $blue;
		color: $light;
		&:hover,
		&:focus {
			border-color: lighten($blue, 20%);
			background: lighten($blue, 20%);
		}
	}
	option {
		color: $dark;
	}
	option:disabled {
		color: lighten($dark, 60%);
	}
}

/* Grid
----------------------------*/
%equal-heights {
	display: flex;
	flex-wrap: wrap;
}
.boxes {
	@extend %equal-heights;
}
.box {
	margin:1em 0.5em;
	width: calc(100% / 4 - 1em);
	@media (max-width: 960px) {
		width: calc(100% / 3 - 1em);
	}
	@media (max-width: 767px) {
		width: calc(100% / 2 - 1em);
	}
	@media (max-width: 600px) {
		width: calc(100% - 1em);
	}
}

/* Thumbs
----------------------------*/
.thumb {
	padding: 1em;
	text-align: center;
	position: relative;
	width: calc(100% - 2em);
	max-width: 12em;
	margin: auto;
	border: 1px solid darken($light, 10%);
	background: $light;
	box-shadow: 0px 4px 4px -4px $dark;
	border-radius: 4px;
	transition: background 800ms ease;
	opacity: 1;
	transform: scale(1);
	animation: show 500ms 1 ease-in-out;
	@keyframes show {
		from {
			transform:scale(0.5);
			opacity: 0;
		}
	}
	img {
		max-width: 100%;
		padding: 1em;
		width: calc(100% - 2em);
	}
	.img-loading {
    width: 100%;
    margin: auto;
    text-align:center;
    position:relative;
    color: $blue;
    div{
      display: block;
      width: 100%;
      min-height: 190px;
      margin: auto;
      background: url(data:image/svg+xml;base64,<?xml version="1.0" encoding="UTF-8" standalone="no"?><!-- Generator: Gravit.io --><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" style="isolation:isolate" viewBox="0 0 84 150" width="84pt" height="150pt"><mask id="_mask_xufmVbcGXQQ67q20xJofSOfuCj7MrVwb" x="-200%" y="-200%" width="400%" height="400%"><rect x="-200%" y="-200%" width="400%" height="400%" style="fill:white;"/><line x1="8.573" y1="17.5" x2="74.573" y2="17.5" fill="black" stroke="none"/></mask><line x1="8.573" y1="17.5" x2="74.573" y2="17.5" mask="url(#_mask_xufmVbcGXQQ67q20xJofSOfuCj7MrVwb)" vector-effect="non-scaling-stroke" stroke-width="10" stroke="rgb(34,34,34)" stroke-linejoin="miter" stroke-linecap="round" stroke-miterlimit="4"/><mask id="_mask_klHQNNClY4jTyXmuDtpEjvrt9iORqond" x="-200%" y="-200%" width="400%" height="400%"><rect x="-200%" y="-200%" width="400%" height="400%" style="fill:white;"/><path d=" M 8.573 48.033 L 74.573 48.033 M 8.573 74.665 L 74.573 74.665 M 8.573 99.965 L 74.573 99.965 M 8.573 124 L 74.573 124 M 8.573 20 L 8.573 129 M 30.573 20 L 30.573 129 M 52.573 20 L 52.573 129 M 74.573 20 L 74.573 129" fill-rule="evenodd" fill="black" stroke="none"/></mask><path d=" M 8.573 48.033 L 74.573 48.033 M 8.573 74.665 L 74.573 74.665 M 8.573 99.965 L 74.573 99.965 M 8.573 124 L 74.573 124 M 8.573 20 L 8.573 129 M 30.573 20 L 30.573 129 M 52.573 20 L 52.573 129 M 74.573 20 L 74.573 129" fill-rule="evenodd" fill="rgb(0,0,0)" mask="url(#_mask_klHQNNClY4jTyXmuDtpEjvrt9iORqond)" vector-effect="non-scaling-stroke" stroke-width="4" stroke="rgb(34,34,34)" stroke-linejoin="miter" stroke-linecap="round" stroke-miterlimit="4"/><path d=" M 8.573 48.033 L 74.573 48.033 M 8.573 74.665 L 74.573 74.665 M 8.573 99.965 L 74.573 99.965 M 8.573 124 L 74.573 124 M 8.573 20 L 8.573 129 M 30.573 20 L 30.573 129 M 52.573 20 L 52.573 129 M 74.573 20 L 74.573 129" fill-rule="evenodd" fill="rgb(0,0,0)"/><path d=" M 49.573 8 C 49.573 6.344 50.917 5 52.573 5 C 54.229 5 55.573 6.344 55.573 8 C 55.573 9.656 54.229 11 52.573 11 C 50.917 11 49.573 9.656 49.573 8 Z  M 27.573 8 C 27.573 6.344 28.917 5 30.573 5 C 32.229 5 33.573 6.344 33.573 8 C 33.573 9.656 32.229 11 30.573 11 C 28.917 11 27.573 9.656 27.573 8 Z  M 6.073 8 C 6.073 6.344 7.417 5 9.073 5 C 10.729 5 12.073 6.344 12.073 8 C 12.073 9.656 10.729 11 9.073 11 C 7.417 11 6.073 9.656 6.073 8 Z  M 71.573 8 C 71.573 6.344 72.917 5 74.573 5 C 76.229 5 77.573 6.344 77.573 8 C 77.573 9.656 76.229 11 74.573 11 C 72.917 11 71.573 9.656 71.573 8 Z " fill-rule="evenodd" fill="none" vector-effect="non-scaling-stroke" stroke-width="1" stroke="rgb(0,0,0)" stroke-linejoin="miter" stroke-linecap="butt" stroke-miterlimit="4"/><path d=" M 10.698 139.279 L 10.698 139.279 L 10.698 139.279 Q 10.698 140.944 10.173 141.766 L 10.173 141.766 L 10.173 141.766 Q 9.647 142.588 8.566 142.588 L 8.566 142.588 L 8.566 142.588 Q 7.529 142.588 6.989 141.746 L 6.989 141.746 L 6.989 141.746 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141.766 Q 53.647 142.588 52.566 142.588 L 52.566 142.588 L 52.566 142.588 Q 51.529 142.588 50.989 141.746 L 50.989 141.746 L 50.989 141.746 Q 50.448 140.905 50.448 139.279 L 50.448 139.279 L 50.448 139.279 Q 50.448 137.6 50.971 136.787 L 50.971 136.787 L 50.971 136.787 Q 51.494 135.974 52.566 135.974 L 52.566 135.974 L 52.566 135.974 Q 53.612 135.974 54.155 136.822 L 54.155 136.822 L 54.155 136.822 Q 54.698 137.67 54.698 139.279 Z  M 51.187 139.279 L 51.187 139.279 L 51.187 139.279 Q 51.187 140.681 51.516 141.32 L 51.516 141.32 L 51.516 141.32 Q 51.846 141.959 52.566 141.959 L 52.566 141.959 L 52.566 141.959 Q 53.296 141.959 53.623 141.311 L 53.623 141.311 L 53.623 141.311 Q 53.951 140.663 53.951 139.279 L 53.951 139.279 L 53.951 139.279 Q 53.951 137.895 53.623 137.251 L 53.623 137.251 L 53.623 137.251 Q 53.296 136.607 52.566 136.607 L 52.566 136.607 L 52.566 136.607 Q 51.846 136.607 51.516 137.242 L 51.516 137.242 L 51.516 137.242 Q 51.187 137.877 51.187 139.279 Z  M 76.698 139.279 L 76.698 139.279 L 76.698 139.279 Q 76.698 140.944 76.173 141.766 L 76.173 141.766 L 76.173 141.766 Q 75.647 142.588 74.566 142.588 L 74.566 142.588 L 74.566 142.588 Q 73.529 142.588 72.989 141.746 L 72.989 141.746 L 72.989 141.746 Q 72.448 140.905 72.448 139.279 L 72.448 139.279 L 72.448 139.279 Q 72.448 137.6 72.971 136.787 L 72.971 136.787 L 72.971 136.787 Q 73.494 135.974 74.566 135.974 L 74.566 135.974 L 74.566 135.974 Q 75.612 135.974 76.155 136.822 L 76.155 136.822 L 76.155 136.822 Q 76.698 137.67 76.698 139.279 Z  M 73.187 139.279 L 73.187 139.279 L 73.187 139.279 Q 73.187 140.681 73.516 141.32 L 73.516 141.32 L 73.516 141.32 Q 73.846 141.959 74.566 141.959 L 74.566 141.959 L 74.566 141.959 Q 75.296 141.959 75.623 141.311 L 75.623 141.311 L 75.623 141.311 Q 75.951 140.663 75.951 139.279 L 75.951 139.279 L 75.951 139.279 Q 75.951 137.895 75.623 137.251 L 75.623 137.251 L 75.623 137.251 Q 75.296 136.607 74.566 136.607 L 74.566 136.607 L 74.566 136.607 Q 73.846 136.607 73.516 137.242 L 73.516 137.242 L 73.516 137.242 Q 73.187 137.877 73.187 139.279 Z " fill-rule="evenodd" fill="rgb(0,0,0)"/></svg>)
        no-repeat center center transparent;
      animation: flash 800ms infinite ease-in-out;
      @keyframes flash {
        from {
          opacity: 0;
        }
      }
    }
  }
	figcaption {
		margin-top: 0.2em;
		font-size: 12px;
		font-weight: 700;
		color: darken($light, 30%);
	}
	&.hide {
		opacity: 0;
		transform: scale(0.2);
		animation: hideElement 200ms 1 ease-in-out;
		@keyframes hideElement {
			from {
				transform:scale(1);
				opacity: 1;
			}
		}
	}
	.img-close {
		position: absolute;
		top: -8px;
		right: -8px;
		width: 30px;
		height: 30px;
		line-height: 1.2;
		font-size: 25px;
		font-weight: bold;
		border-radius: 100%;
		cursor: pointer;
		background: $red;
		border: 1px solid darken($red, 20%);
		color: $light;
	}
}
.exists{
	border:1px solid $red;
	background:lighten($red,20%);
	transition: background 800ms ease;
	figcaption{
		color:$light;
	}
}
/* layout
----------------------------*/
.header {
	text-align: center;
	h3 {
		margin: 0;
		font-size: 2em;
		color: darken($light, 50%);
	}
}
!

JS 

              
                const {useState, useEffect, Fragment } = React;

const assetsUrl = "http://ukulala.surge.sh/chords";
/**
 * Storage theme settings
 *
 * set Storage.val = {color: 'blue'}
 * get Storage.val
 */
const Storage = {
	get val() {
		this.data = window.localStorage.getItem("demo_data");
		return JSON.parse(this.data);
	},
	set val(value) {
		this.data = JSON.stringify(value);
		window.localStorage.setItem("demo_data", this.data);
	}
};

// check array duplicates
const hasDuplicates = array => {
	return (new Set(array)).size !== array.length;
}


/* Notes
-----------------------------*/
const Notes = {
	C: "Do",
	Db: "Reb/Do#",
	D: "Re",
	Eb: "Mib/Re#",
	E: "Mi",
	F: "Fa",
	Gb: "Solb/Fa#",
	G: "Sol",
	Ab: "Lab/Sol#",
	A: "La",
	Bb: "Sib/La#",
	B: "Si"
};
/* Tonalityes
-----------------------------*/
const Tonalityes = {
	"": "",
	m: "m",
	_: "+",
	"5": "5",
	"6": "6",
	maj7: "maj7",
	m7: "m7",
	m6: "m6",
	m7_b5_: "m7(b5)",
	dim7: "dim7",
	"7": "7",
	"9": "9",
	"7_b9_": "7(b9)",
	"7__5_": "7(#5)"
};
/* Simple forms component
-----------------------------*/
const Form = (props) => <form onSubmit={props.fn}>{props.children}</form>;
const Select = (props) => {
	let data = props.data;
	let notes = {};
	if (props.sort) notes = Object.entries(data).sort();
	else notes = Object.entries(data);
	return (
		<select onChange={props.fn}>
			{notes.map(([key, value]) => (
				<option key={key} value={key}>
					{value}
				</option>
			))}
		</select>
	);
};
const Submit = (props) => <input type="submit" value={props.val || "Get"} />;

/* Columns
-----------------------------*/
const Boxes = (props) => <div className="boxes">{props.children}</div>;
const Box = (props) => <div className="box">{props.children}</div>;
const ImgLoader = () => <div className="img-loading"><div></div></div>

/* Image
-----------------------------*/
const Image = (props) => {
	const [src, setSrc] = useState("");
	// use timeout and show image
	useEffect(() => {
		let timerid = false;
		if (timerid) {
			clearTimeout(timerid);
		}
		timerid = setTimeout(() => {
			setSrc(`${assetsUrl}/${props.data}.svg`);
		}, 100);
	}, [props.data]);

	return (
		<figure className={`thumb ${props.data}`}>
			<span className="img-close" onClick={props.fn}>&times;</span>
			{/* check if exists src */}
			{src ? <img src={src} /> : <ImgLoader/>}
			<figcaption>
        {props.data.substring(0, 2).charAt(1) === "b"
          ? Notes[props.data.substring(0, 2)] +
            " " +
            Tonalityes[props.data.substring(2, props.data.length)]
          : Notes[props.data.substring(0, 1)] +
            " " +
            Tonalityes[props.data.substring(1, props.data.length)]}
			</figcaption>
		</figure>
	);
};

const Header = (props) => (
	<header className="header">
		<h3>{props.children}</h3>
	</header>
);

const App = () => {
	// last array
	let lastSaved = Storage.val ? Storage.val : ["C"];
	// data of chords
	const [data, setData] = useState(["C"]);

	// note & tonality
	const [note, setNote] = useState("C");
	const [tonality, setTonality] = useState("");

	// on init get last data saved
	useEffect(() => setData(lastSaved), []);
	
	// Add submit
	const handleSubmit = (e) => {
    e.preventDefault();
    let arr = note + tonality;
    let newArr = [...data, arr];
    if (hasDuplicates(newArr)) {
      // if chord exists show red color
      let img = document.querySelector(`.${arr}`);
      img.classList.add("exists");
      let w = setTimeout(() => {
        img.classList.remove("exists");
        clearTimeout(w);
      }, 800);
    }
    // update array of unique elements
    setData([...new Set(newArr)]);
    Storage.val = [...new Set(newArr)];
		return false;
	};

	// delete data
	const removeData = (evt, index) => {
		let element = evt.target.parentNode;
		element.classList.add("hide");

		let w = setTimeout(() => {
			// remove array by index
			let arr = [...data];
			arr.splice(index, 1);
			// remove duplicates
			let savedArr = [...new Set(arr)];
			// update
			setData(savedArr);
			// storage saved
			Storage.val = savedArr;
			clearTimeout(w);
		}, 500);

	};

	return (
		<Fragment>
			<Header>Ukelele Componser</Header>
			<Form fn={handleSubmit}>
				<Select 
					sort={false} 
					fn={(e) => setNote(e.target.value)} 
					data={Notes} />
				<Select
					sort={true}
					fn={(e) => setTonality(e.target.value)}
					data={Tonalityes}
				/>
				<Submit val="+" />
			</Form>
			<Boxes>
				{data.map((item, index) => (
					<Box key={index}>
						<Image 
							fn={(evt) => removeData(evt, index)} 
							data={item} />
					</Box>
				))}
			</Boxes>
		</Fragment>
	);
};

ReactDOM.render(<App />, window.root);
!
999px

Console