styles.css

* {
    box-sizing: border-box;
}

html, body {
    margin: 0;
}

body {
    font-size: 16px;
}

:root {
    --primary: #2196f3;
}

[data-template] {
    display: none;
}

.container {
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.button {
    padding: 10px 15px;
    background-color: var(--primary);
    border: none;
    border-radius: 4px;
    color: #fff;
    font-weight: bold;
}

.tasks {
    padding: 0;
    margin: 0;
    list-style: none;
}

.task {
    height: 40px;
    font-size: 18px;
    cursor: pointer;
}

.task-done {
    text-decoration: line-through
}

.new-task-text {
    display: block;
    width: 100%;
    height: 50px;
    padding-left: 16px;
    padding-right: 16px;
    border: 1px solid #ccc;
    border-radius: 4px;
}

.add-button {
    margin-top: 16px;
    cursor: pointer;
}