style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.wrapper{
    width: 100%;
    height: 100vh;
    background:linear-gradient(135deg,green,blue);
    padding: 10px;
}

.todo-app{
    width: 100%;
    max-width: 540px;
    background-color: white;
    margin: 100px auto 20px;
    padding: 40px 30px 70px;
    border-radius: 10px;
}

.search-box{
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: 20px;
}
.search-box input{
    flex: 1;
    position: relative;
    padding:5px 30px 5px 30px;
    border-radius: 20px;
    background-color: lightgrey;
}
.search-box button{
    position: absolute;
    right: 33%;
    border-radius: 20px;
    background-color: red;
    color: white;
    padding:5px 20px 5px 20px;
    cursor: pointer;
}
ul li{
    list-style: none;
    padding: 12px 8px 12px 50px;
    user-select: none;
    cursor: pointer;
    position: relative;
}

ul li::before{
    content: "";
    position: absolute;
    height: 28px;
    width: 28px;
    border-radius: 50%;
    background-color: lightblue;
    top: 12px;
    left: 8px;
}

ul li.checked{
    color: black;
    text-decoration: line-through;
}

ul li.checked::before{
    background-color: rgb(12, 14, 14);
}

ul li span{
    position: absolute;
    right: 0;
    top: 10px;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    text-align: center;
}

ul li span:hover{
    cursor: pointer;
    background-color: lightblue;
}