style.css

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

html,
body {
    width: 100%;
    height: 100%;
}

main {
    width: 100%;
    min-height: 100vh;
    background: linear-gradient(to bottom, rgba(255, 255, 255, 0.15) 0%, rgba(0, 0, 0, 0.15) 100%), radial-gradient(at top center, rgba(255, 255, 255, 0.40) 0%, rgba(0, 0, 0, 0.40) 120%) #989898;
    background-blend-mode: multiply, multiply;
    display: flex;
    justify-content: center;
    align-items: center;
}

.container {
    background-color: white;
    width: 100%;
    max-width: 30rem;
    max-height: 45rem;
    border-radius: 20px;
}

.title {
    margin-top: .5rem;
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 2rem;
    gap: .5rem;
}

.title img {
    width: 2rem;
    height: 2rem;
}

.title p {
    font-size: 1.5rem;
    font-weight: 400;
}

.row {
    background-color: rgb(194, 194, 194);
    border-radius: 25px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin: .5rem .5rem 1rem 1rem;
}

input{
    flex: 1 ;
    border: none;
    outline: none;
    height: 2rem;
    margin-left: 2rem;
    background: transparent;
}

button{
    border: none;
    background-color: cornflowerblue;
    height: 100%;
    padding: .5rem 1rem;
    border-radius: 25px;
    color: white;
    cursor: pointer;
    font-size: 1rem;
}
ul li{
    list-style: none;
    position: relative;
    user-select: none;
    padding:.5rem 3rem;
}

ul{
    margin: 1rem;
}
ul li::before{
    content: "";
    position: absolute;
    height: 1.5rem;
    width: 1.5rem;
    border-radius: 50%;
    background-image: url("unchecked.png");
    background-size: cover;
    background-position: center ;
    left: 1rem;
    bottom: .5rem;
    cursor: pointer;
}
ul li span{
    text-align: center;
    position: absolute;
    right: 1rem;
    cursor: pointer;
    font-size: 1.3rem;
    width: 2rem;
    height: 2rem;
    border-radius: 50%;
    line-height: 2rem;
}
ul li span:hover{
    background-color: #dbdbdb;
}
ul li.checked{
    color: #989898;
    text-decoration: line-through;
}
ul li.checked::before{
    background-image: url("checked.png");
}
@media screen and (width<=600px) {
    .container {
        width: 100%;
        max-height: 55rem;
    }
    ul li span:hover{
        background-color: transparent;
    }
}