MyTodo.html

<svelte:options tag="my-todo" />

<h1>Todos Svelte</h1>
<section>
  <TodoInput on:add={addTodo}></TodoInput>
  <ul id="list-container">
    {#each items as item, index (item.id)}
      <TodoItem
        bind:checked={item.checked}
        bind:text={item.text}
        on:remove={() => removeTodo(index)}
      ></TodoItem>
    {/each}
  </ul>
</section>

<style>
  :host {
    display: block;
  }

  h1 {
    font-size: 100px;
    font-weight: 100;
    text-align: center;
    color: rgba(175, 47, 47, 0.15);
  }

  section {
    background: #fff;
    margin: 30px 0 40px 0;
    position: relative;
    box-shadow: 0 2px 4px 0 rgba(0, 0, 0, 0.2), 0 25px 50px 0 rgba(0, 0, 0, 0.1);
  }

  #list-container {
    margin: 0;
    padding: 0;
    list-style: none;
    border-top: 1px solid #e6e6e6;                                                    
  }                                                                                   
</style>

<script>
  import TodoInput from './TodoInput.html';
  import TodoItem from './TodoItem.html';

  let uid = 1;

  let items = [
    { id: uid++, checked: false, text: 'my initial todo' },
    { id: uid++, checked: true, text: 'Learn about Web Components' }
  ];

  function addTodo (evt) {
    let text = evt.detail;
    items = [...items, { id: uid++, text, checked: false, }];
  };

  function removeTodo (index) {
    items = [...items.slice(0, index), ...items.slice(index + 1)];
  };

</script>

TodoInput.html

<svelte:options tag="todo-input" />
    
<form on:submit|preventDefault={handleOnSubmit}>
    <input bind:value placeholder="What needs to be done?"/>
</form>
  
<style>
    :host {
        display: block;
    }
    
    form {
        position: relative;
        font-size: 24px;
        border-bottom: 1px solid #ededed;
    }
    
    input {
        padding: 16px 16px 16px 60px;                                                 
        border: none;                                                                 
        background: rgba(0, 0, 0, 0.003);                                             
        position: relative;                                                           
        margin: 0;
        width: 100%;
        font-size: 24px;
        font-family: inherit;
        font-weight: inherit;
        line-height: 1.4em;
        border: 0;
        outline: none;
        color: inherit;
        padding: 6px;
        border: 1px solid #CCC;
        box-shadow: inset 0 -1px 5px 0 rgba(0, 0, 0, 0.2);
        box-sizing: border-box;
    }
</style>

<script>
  import { createEventDispatcher } from 'svelte';

  const dispatch = createEventDispatcher();

  let value = '';

  function handleOnSubmit () {
    if (!value) return;
    dispatch('add', value);
    value = '';
  };
</script>

TodoItem.html

<svelte:options tag="todo-item" />

<li class={ checked ? 'completed' : '' }>
    <input type="checkbox" bind:checked />
    <label>{text}</label>
    <button on:click|preventDefault={handleOnRemove}>x</button>
</li>
    
<style> 
    :host {
        display: block;
    }
        
    li {
        font-size: 24px;
        display: block;
        position: relative;
        border-bottom: 1px solid #ededed;
    }   
        
    li input {
        text-align: center;                                                           
        width: 40px;
        /* auto, since non-WebKit browsers doesn't support input styling */
        height: auto;
        position: absolute;
        top: 9px;
        bottom: 0;
        margin: auto 0;
        border: none;
        /* Mobile Safari */
        -webkit-appearance: none;
        appearance: none; 
        padding: 0; 
        box-shadow: none;
    }

    li input:after {
        content: url('data:image/svg+xml;utf8,<svg%20xmlns%3D"http%3A//www.w3.org/2000/svg"%20width%3D"40"%20height%3D"40"%20viewBox%3D"-10%20-18%20100%20135"><circle%20cx%3D"50"%20cy%3D"50"%20r%3D"50"%20fill%3D"none"%20stroke%3D"%23ededed"%20stroke-width%3D"3"/></svg>');
    }

    li input:checked:after {
        content: url('data:image/svg+xml;utf8,<svg%20xmlns%3D"http%3A//www.w3.org/2000/svg"%20width%3D"40"%20height%3D"40"%20viewBox%3D"-10%20-18%20100%20135"><circle%20cx%3D"50"%20cy%3D"50"%20r%3D"50"%20fill%3D"none"%20stroke%3D"%23bddad5"%20stroke-width%3D"3"/><path%20fill%3D"%235dc2af"%20d%3D"M72%2025L42%2071%2027%2056l-4%204%2020%2020%2034-52z"/></svg>');
    }

    li label {
        white-space: pre;
        word-break: break-word;
        padding: 15px 60px 15px 15px;
        margin-left: 45px;
        display: block;
        line-height: 1.2;
        transition: color 0.4s;
    }

    li.completed label {
        color: #d9d9d9;
        text-decoration: line-through;
    }

    li button,
    li input[type="checkbox"] {
        outline: none;
    }

    li button {
        margin: 0;
        padding: 0;
        border: 0;
        background: none;
        font-size: 100%;
        vertical-align: baseline;
        font-family: inherit;
        font-weight: inherit;
        color: inherit;
        -webkit-appearance: none;
        appearance: none;
        -webkit-font-smoothing: antialiased;
        -moz-font-smoothing: antialiased;
        font-smoothing: antialiased;
    }

    li button {
        position: absolute;
        top: 0;
        right: 10px;
        bottom: 0;
        width: 40px;
        height: 40px;
        margin: auto 0;
        font-size: 30px;
        color: #cc9a9a;
        margin-bottom: 11px;
        transition: color 0.2s ease-out;
    }

    li button:hover {
        color: #af5b5e;
    }

</style>

<script>
  import { createEventDispatcher } from 'svelte';

  const dispatch = createEventDispatcher();

  export let checked;
  export let text;

  function handleOnRemove () {
    dispatch('remove');
  };
</script>