* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins', sans-serif;
}

.container {
    width: 100%;
    min-height: 100vh;
    padding: 10px;
}

.todo-app {
    width: 100%;
    max-width: 540px;
    background: #fff;
    margin: 150px auto 20px;
    padding: 40px 30px 70px;
    border-radius: 50px;
    box-shadow: 0px 0px 30px #afafaf;
}

h2 {
    color: #002765;
    display: flex;
    align-items: center;
    margin-bottom: 50px;
    font-size: 30px;
    position: relative;
}

.todo-app h2 img {
    position: absolute;
    right: 0;
    width: 40px;
    margin-left: 20px;
}

.row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: #fff;
    border: none;
    outline: 3px groove #000;
    outline-offset: 5px;
    border-radius: 30px;
    padding-left: 20px;
    margin-bottom: 25px;
    box-shadow: 0px 0px 10px #5d5d5d;
}

.row input {
    flex: 1; /* text full available width */
    border: none;
    outline: none;
    padding: 10px;
    background: transparent;
    font-size: 18px;
    font-weight: 600;
    letter-spacing: 1px;
}

.row input::placeholder {
    color: #1e008d;
}

.row button {
    border: none;
    outline: none;
    padding: 16px 30px;
    background: #26068f;
    color: #fff;
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    border-radius: 30px;
    margin: 1px;
}

ul li {
    list-style: none;
    font-size: 18px;
    font-weight: 500;
    letter-spacing: 1px;
    padding: 12px 8px 12px 50px;
    user-select: none;
    cursor: pointer;
    position: relative;
    margin-block: 10px;
}

ul li::before {
    content: '';
    position: absolute;
    height: 30px;
    width: 30px;
    border-radius: 50%;
    background: url(images/unchecked.png);
    background-size: cover;
    background-position: center;
    top: 12px;
    left: 8px;
}

ul li.checked {
    background: #3700a4;
    color: #fff;
    border-radius: 50px;
}

ul li.checked::before {
    background: url(images/checked.png);
    background-size: cover;
}

ul li span {
    position: absolute;
    top: 10px;
    margin-right: 5px;
    width: 30px;
    height: 30px;
    font-size: 22px;
    color: #000;
    line-height: 30px;
    text-align: center;
    border-radius: 50%;
}

ul li.checked span {
    color: #ffffff;
}

ul li.checked span:hover {
    background: #fff;
    color: #000;
}

ul li span:hover {
    background: #000;
    color: #fff;
}

/* Responsive Styles */
@media (max-width: 768px) {
    .todo-app {
        padding: 30px 20px 60px;
        border-radius: 30px;
    }

    h2 {
        font-size: 26px;
        margin-bottom: 40px;
    }

    .row {
        flex-direction: column;
        padding: 10px 15px;
    }

    .row button {
        width: 100%;
        margin-top: 15px;
        padding: 14px;
        font-size: 16px;
    }

    ul li {
        font-size: 16px;
        padding: 10px 8px 10px 40px;
    }

    ul li::before {
        height: 25px;
        width: 25px;
        top: 10px;
        left: 5px;
    }

    ul li span {
        width: 25px;
        height: 25px;
        font-size: 18px;
        line-height: 25px;
    }
}

@media (max-width: 480px) {
    .todo-app {
        padding: 20px 15px 50px;
        border-radius: 20px;
    }

    h2 {
        font-size: 22px;
        margin-bottom: 30px;
    }

    .row button {
        padding: 12px;
        font-size: 14px;
    }

    ul li {
        font-size: 14px;
        padding: 8px 6px 8px 35px;
    }

    ul li::before {
        height: 20px;
        width: 20px;
        top: 8px;
        left: 5px;
    }

    ul li span {
        width: 20px;
        height: 20px;
        font-size: 16px;
        line-height: 20px;
    }
}