index.css

* {
    box-sizing: border-box;
}
html, body {
    margin: 0;
    padding: 0;
    background-color: #FFFDFE;
    font-family: 'Inter', sans-serif;
}
h1 {
    margin-block:0.6em;
    text-align: center;
}
p {
    font-size: 12px;
    color: #2B283A;
    font-weight: 500;
}
.color-scheme, .color-parent, .color-options {
    display: flex;
}
.color-options, main {
    max-width: 550px;
}
.color-options {
    padding-top: 0.5em;
    align-items: center;
    justify-content: space-around;
    height: 3em;
    margin-inline: auto;
    margin-bottom: 0.5em;
    color: #111827;
}
input {
    height: 42px;
    width: 61px;
}
#schemes {
    width: 312px;
    height: 42px;
    font-size: 16px;
}
button {
    max-width: 123px;
    height: 42px;
    font-size: 12px;
    background-color: #FFFFFF;
    border: 1px solid #D1D5DB;
    box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.05);
    border-radius: 4px;
    color: #374151;
    cursor: pointer;
}
.color-scheme {
    height: 100%;
    margin-inline: auto;
}
.color-parent {
    width: 20%;
    height: 100%;
    flex-direction: column;   
}
main {
    height: 85%;
    margin-inline: auto;
    border-radius: 5px;
    box-shadow: rgba(0, 0, 0, 0.35) 0px 5px 15px;
}
.color-parent > p {
    margin: 0;
    text-align: center;
    padding-block: 1em;
}
.color {
    width: 100%;
    height: 81%;
}
#color-one {
    background-color: #F55A5A;
}
#color-two {
    background-color: #2B283A;
}
#color-three {
    background-color: #FBF3AB;
}
#color-four {
    background-color: #AAD1B6;
}
#color-five {
    background-color: #A626D3;
}

@media (max-width: 590px) {
    h1 {
        font-size: 1.2em;
        padding: 0.6em;
        margin-top: 0.5em;
    }
    body {
        padding: 1em;
    }
    main {
        padding: 0.7em;
    }
    #color-input, #schemes {
        margin-right: 10px;
    }
}

@media (max-width: 350px) {
    p, button {
        font-size: 10px;
    }
    #schemes {
        font-size: 12px;
    }
}