style.css

:root {
    --primary-color: indianred;
}

body {
    background-color: var(--primary-color);
}

*,
*:before,
*:after {
    padding: 0;
    margin: 0;
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
}

.container {
    margin: auto;
    min-width: 40vh;
    padding: 2rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    border:3px solid  white;
    height: 100vh;
}

.header {
    margin:0 0 2rem 0;
    color: white;
    padding: 1rem;
}

.main{
     margin-bottom: 3rem;
     display:flex;
     justify-content: center;
     align-self:center;
 }

.textarea {
    min-width: 40vh;
    padding: 0.5rem 0.5rem;
}

.btn {
    margin-left: 2rem;
    padding: 0.60rem 1rem;
    text-align: center;
    color: #ffffff;
    border-radius: 5px;
    cursor: pointer;
    border-color: white;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
}


.error-box {
    padding-top: 2rem;
    text-align: center;
    min-height: 1.5rem;
    color: white;

}

.tasks {
    min-width: 50vh;
    background-color: #ffffff;
    -webkit-box-shadow: 0 15px 30px rgba(0, 0, 0, 0.3);
    box-shadow: 0 15px 30px rgba(0, 0, 0, 0.3);
    padding: 1rem 2rem;
    border-radius: 5px;
}

.task {
    min-width: 50vh;
    background: #ffffff;
    min-height:2vh;
    padding: 5px 10px;
    border-radius: 0px;
    margin-top: 10px;
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    -webkit-box-align: center;
    -ms-flex-align: center;
    align-items: center;
    -webkit-box-pack: justify;
    -ms-flex-pack: justify;
    justify-content: space-between;
    cursor: pointer;
    border-bottom: 2px solid #d1d3d4;
}

.task span {
    font-family: 'Poppins', sans-serif;
    font-size: 15px;
    font-weight: 400;
    cursor: pointer;
}

.task button {
    border: none;
    height: 100%;
    width: 40px;
    color: #ffffff;
    border-radius: 5px;
    cursor: pointer;
    border-color: white;
}

.completed {
    text-decoration: line-through;
}

.delete {
    background-color: var(--primary-color);
}