responsive slider with ul li elements - html

Question

there is full code of my plugin > https://codepen.io/doodlemarks/pen/aFcly
in my code element #slider ul li have width bigger than 900px and it is not scaling smaller on device with smaller resolution.
can anyone help me how to improve it and make it responsible to scale ul li element on devices e.g. mobile?
html/css:
#import url(https://fonts.googleapis.com/css?family=Open+Sans:400,300,600);
html {
border-top: 5px solid #fff;
background: #58DDAF;
color: #2a2a2a;
}
html, body {
margin: 0;
padding: 0;
font-family: 'Open Sans';
}
h1 {
color: #fff;
text-align: center;
font-weight: 300;
}
#slider {
position: relative;
overflow: hidden;
margin: 20px auto 0 auto;
border-radius: 4px;
}
#slider ul {
position: relative;
margin: 0;
padding: 0;
height: 200px;
list-style: none;
}
#slider ul li {
position: relative;
display: block;
float: left;
margin: 0;
padding: 0;
width: 500px;
height: 300px;
background: #ccc;
text-align: center;
line-height: 300px;
}
a.control_prev, a.control_next {
position: absolute;
top: 40%;
z-index: 999;
display: block;
padding: 4% 3%;
width: auto;
height: auto;
background: #2a2a2a;
color: #fff;
text-decoration: none;
font-weight: 600;
font-size: 18px;
opacity: 0.8;
cursor: pointer;
}
a.control_prev:hover, a.control_next:hover {
opacity: 1;
-webkit-transition: all 0.2s ease;
}
a.control_prev {
border-radius: 0 2px 2px 0;
}
a.control_next {
right: 0;
border-radius: 2px 0 0 2px;
}
.slider_option {
position: relative;
margin: 10px auto;
width: 160px;
font-size: 18px;
}
<h1>Incredibly Basic Slider</h1>
<div id="slider">
>
<
<ul>
<li>SLIDE 1</li>
<li style="background: #aaa;">SLIDE 2</li>
<li>SLIDE 3</li>
<li style="background: #aaa;">SLIDE 4</li>
</ul>
</div>
<div class="slider_option">
<input type="checkbox" id="checkbox">
<label for="checkbox">Autoplay Slider</label>
</div>

Answer 1

You can use #media CSS at-rule in your code just for example
<style>
/* First Example */
/* For desktop: */
.col-1 {width: 8.33%;}
.col-2 {width: 16.66%;}
.col-3 {width: 25%;}
#media only screen and (max-width: 768px) {
/* For mobile phones: */
[class*="col-"] {
width: 100%;
}
}
/* Second Example */
#media screen and (min-width: 900px) {
article {
padding: 1rem 3rem;
}
}
</style>
You can learn more about responsive web by these links
https://www.w3schools.com/css/css_rwd_intro.asp
https://developer.mozilla.org/en-US/docs/Web/CSS/#media