water.css (dark theme) 

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto",
        "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans",
        "Helvetica Neue", sans-serif;
    line-height: 1.4;
    max-width: 800px;
    margin: 20px auto;
    padding: 0 10px;
    color: #dbdbdb;
    background: #202b38;
    text-rendering: optimizeLegibility;
}

button,
input,
textarea {
    transition: background-color 0.1s linear, border-color 0.1s linear,
        color 0.1s linear, box-shadow 0.1s linear, transform 0.1s ease;
}

h1 {
    font-size: 2.2em;
    margin-top: 0;
}

h1,
h2,
h3,
h4,
h5,
h6 {
    margin-bottom: 12px;
}

h1,
h2,
h3,
h4,
h5,
h6,
strong {
    color: #fff;
}

h1,
h2,
h3,
h4,
h5,
h6,
b,
strong,
th {
    font-weight: 600;
}

button,
input[type="submit"],
input[type="button"],
input[type="checkbox"] {
    cursor: pointer;
}

input:not([type="checkbox"]),
select {
    display: block;
}

input,
select,
button,
textarea {
    color: #fff;
    background-color: #161f27;
    font-family: inherit;
    font-size: inherit;
    margin-right: 6px;
    margin-bottom: 6px;
    padding: 10px;
    border: none;
    border-radius: 6px;
    outline: none;
}

input:not([type="checkbox"]),
select,
button,
textarea {
    -webkit-appearance: none;
}

textarea {
    margin-right: 0;
    width: 100%;
    box-sizing: border-box;
    resize: vertical;
}

button,
input[type="submit"],
input[type="button"] {
    padding-right: 30px;
    padding-left: 30px;
}

button:hover,
input[type="submit"]:hover,
input[type="button"]:hover {
    background: #324759;
}

input:focus,
select:focus,
button:focus,
textarea:focus {
    box-shadow: 0 0 0 2px rgba(0, 150, 191, 0.670588);
}

input[type="checkbox"]:active,
input[type="submit"]:active,
input[type="button"]:active,
button:active {
    transform: translateY(2px);
}

input:disabled {
    cursor: not-allowed;
    opacity: 0.5;
}

::placeholder {
    color: #a9a9a9;
}

a {
    text-decoration: none;
    color: #41adff;
}

a:hover {
    text-decoration: underline;
}

code,
kbd {
    background: #161f27;
    color: #ffbe85;
    padding: 5px;
    border-radius: 6px;
}

pre > code {
    padding: 10px;
    display: block;
    overflow-x: auto;
}

img {
    max-width: 100%;
}

hr {
    border: none;
    border-top: 1px solid #dbdbdb;
}

table {
    border-collapse: collapse;
    margin-bottom: 10px;
    width: 100%;
}

td,
th {
    padding: 6px;
}

table,
th,
td {
    border: 1px solid #dbdbdb;
}