style.css

:root
{
    --default-color : #e3f9ff;
    --calculator-color : #3a4452;
    --white : #fff;
    --heading-color : rgb(98, 255, 0);
    --btns-color : #33ffd8;
    --link-color : rgb(128, 255, 0);
}

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

h1
{
    background-color: var(--default-color);
    position: absolute;
    padding-top: 25px;
    text-decoration: underline;
    cursor: pointer;
    right: 43.3%;
}

h1:hover
{
    padding-top: 10px;
    color: var(--calculator-color);
    transition: all ease 0.5s;
}

.calculator-container
{
    padding-top: 30px;
    width: 100%;
    height: 100vh;
    background-color: var(--default-color);
    display: flex;
    align-items: center;
    justify-content: center;
}

.calculator
{
    background-color: var(--calculator-color);
    padding: 20px;
    border-radius: 10px;
}

.calculator form#calculator-form input
{
    border: 0;
    outline: 0;
    width: 60px;
    height: 60px;
    border-radius: 10px;
    box-shadow: -8px -8px 15px rgba(255, 255, 255, 0.1),5px 5px 15px rgba(0 , 0 , 0 , 0.2);
    background: transparent;
    font-size: 20px;
    color : var(--white);
    cursor: pointer;
    margin: 10px;
}

.calculator form#calculator-form .display-screen
{
    display: flex;
    justify-content: flex-end;
    margin: 20px 0;
}

.calculator form#calculator-form .display-screen input
{
    text-align: right;
    flex: 1;
    font-size: 45px;
    box-shadow: none;
}

.calculator form#calculator-form input.equal-btn
{
    width: 145px;
}

.calculator form#calculator-form input.btn-imp
{
    color: var(--btns-color);
}

.calculator form#calculator-form input:not(.calculator form#calculator-form .display-screen input):hover
{
    color: var(--btns-color);
    box-shadow: -8px -8px 15px rgba(255, 255, 255, 0.304),5px 5px 15px rgba(0, 0, 0, 0.277);
}

p.hidden
{
    display: none;
}

p.hidden marquee
{
    font-size: 32px;
}

p.hidden a 
{
    text-decoration: none;
    color: var(--link-color);
}