Теперь я понимаю, что Codepen не был вашим, проблема в том, что у вас нет необходимой установки Sass для компиляции того же кода из Codepen локально.
Использование конвертера , вы можете легко конвертировать чужой Sass в стандартный CSS и использовать его для своего собственного проекта:
.navigation__checkbox {
display: none;
}
.navigation__button {
background-color: #fff;
height: 7rem;
width: 7rem;
border-radius: 50%;
position: fixed;
top: 4rem;
right: 6rem;
z-index: 2000;
box-shadow: 0 1rem 3rem rgba(0, 0, 0, 0.2);
text-align: center;
cursor: pointer;
}
.navigation__background {
height: 6rem;
width: 6rem;
border-radius: 50%;
position: fixed;
top: 4.5rem;
right: 6.5rem;
background-image: radial-gradient(#2998ff, #5643fa);
z-index: 1000;
transition: transform 0.8s cubic-bezier(0.86, 0, 0.07, 1);
}
.navigation__nav {
height: 100vh;
position: fixed;
top: 0;
left: 0;
z-index: 1500;
opacity: 0;
width: 0;
transition: all 0.8s cubic-bezier(0.68, -0.55, 0.265, 1.55);
}
.navigation__list {
list-style: none;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
text-align: center;
width: 100%;
}
.navigation__link:link,
.navigation__link:visited {
display: inline-block;
font-size: 3rem;
font-weight: 300;
padding: 1rem 2rem;
color: #fff;
text-decoration: none;
text-transform: uppercase;
background-image: linear-gradient(120deg, transparent 0%, transparent 50%, #fff 50%);
background-size: 230%;
transition: all 0.4s;
}
.navigation__link:hover,
.navigation__link:active {
background-position: 100%;
color: #2998ff;
transform: translateX(1rem);
}
.navigation__checkbox:checked~.navigation__background {
transform: scale(80);
}
.navigation__checkbox:checked~.navigation__nav {
opacity: 1;
width: 100%;
}
.navigation__icon {
position: relative;
margin-top: 3.5rem;
}
.navigation__icon,
.navigation__icon::before,
.navigation__icon::after {
width: 3rem;
height: 2px;
background-color: #333;
display: inline-block;
}
.navigation__icon::before,
.navigation__icon::after {
content: "";
position: absolute;
left: 0;
transition: all 0.2s;
}
.navigation__icon::before {
top: -0.8rem;
}
.navigation__icon::after {
bottom: -0.8rem;
}
.navigation__button:hover .navigation__icon::before {
top: -1rem;
}
.navigation__button:hover .navigation__icon::after {
bottom: -1rem;
}
.navigation__checkbox:checked+.navigation__button .navigation__icon {
background-color: transparent;
}
.navigation__checkbox:checked+.navigation__button .navigation__icon::before {
transform: rotate(135deg);
top: 0;
}
.navigation__checkbox:checked+.navigation__button .navigation__icon::after {
transform: rotate(-135deg);
bottom: 0;
}
<div class="navigation">
<input type="checkbox" class="navigation__checkbox" id="navi-toggle">
<label for="navi-toggle" class="navigation__button">
<span class="navigation__icon"> </span>
</label>
<div class="navigation__background"> </div>
<nav class="navigation__nav">
<ul class="navigation__list">
<li class="navigation__item"><a href="#" class="navigation__link">Home</a> </li>
<li class="navigation__item"><a href="#" class="navigation__link">About us</a> </li>
<li class="navigation__item"><a href="#" class="navigation__link">Careers</a> </li>
<li class="navigation__item"><a href="#" class="navigation__link">Projects</a> </li>
<li class="navigation__item"><a href="#" class="navigation__link">Contact Us</a> </li>
</ul>
</nav>
</div>