GP CSS gets destroyed by Simple CSS

Here is the css I put in "Simple CSS" for this specific page:

.timeline{
--uiTimelineMainColor: var(--timelineMainColor, #222);
--uiTimelineSecondaryColor: var(--timelineSecondaryColor, #fff);

position: relative;
padding-top: 3rem;
padding-bottom: 3rem;
}

.timeline:before{
content: "";
width: 4px;
height: 100%;
background-color: var(--uiTimelineMainColor);

position: absolute;
top: 0;
}

.timeline__group{
position: relative;
}

.timeline__group:not(:first-of-type){
margin-top: 4rem;
}

.timeline__year{
padding: .5rem 1.5rem;
color: var(--uiTimelineSecondaryColor);
background-color: var(--uiTimelineMainColor);

position: absolute;
left: 0;
top: 0;
}

.timeline__box{
position: relative;
}

.timeline__box:not(:last-of-type){
margin-bottom: 30px;
}

.timeline__box:before{
content: "";
width: 100%;
height: 2px;
background-color: var(--uiTimelineMainColor);

position: absolute;
left: 0;
z-index: -1;
}

.timeline__date{
min-width: 65px;
position: absolute;
left: 0;

box-sizing: border-box;
padding: .5rem 1.5rem;
text-align: center;

background-color: var(--uiTimelineMainColor);
color: var(--uiTimelineSecondaryColor);
}

.timeline__day{
font-size: 2rem;
font-weight: 700;
display: block;
}

.timeline__month{
display: block;
font-size: .8em;
text-transform: uppercase;
}

.timeline__post{
padding: 1.5rem 2rem;
border-radius: 2px;
border-left: 3px solid var(--uiTimelineMainColor);
box-shadow: 0 1px 3px 0 rgba(0, 0, 0, .12), 0 1px 2px 0 rgba(0, 0, 0, .24);
background-color: var(--uiTimelineSecondaryColor);
}

@media screen and (min-width: 641px){

.timeline:before{
left: 30px;
}

.timeline__group{
padding-top: 55px;
}

.timeline__box{
padding-left: 80px;
}

.timeline__box:before{
top: 50%;
transform: translateY(-50%);
}

.timeline__date{
top: 50%;
margin-top: -27px;
}
}

@media screen and (max-width: 640px){

.timeline:before{
left: 0;
}

.timeline__group{
padding-top: 40px;
}

.timeline__box{
padding-left: 20px;
padding-top: 70px;
}

.timeline__box:before{
top: 90px;
}

.timeline__date{
top: 0;
}
}

.timeline{
--timelineMainColor: #4557bb;
font-size: 16px;
}

@media screen and (min-width: 768px){

html{
font-size: 62.5%;
}
}

@media screen and (max-width: 767px){

html{
font-size: 55%;
}
}

/*
* demo page
*/

body{
font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, Open Sans, Ubuntu, Fira Sans, Helvetica Neue, sans-serif;
font-size: 1.6rem;
color: #222;

background-color: #fff;
margin: 0;
-webkit-overflow-scrolling: touch;
overflow-y: scroll;
}

p{
margin-top: 0;
margin-bottom: 1.5rem;
line-height: 1.5;
}

p:last-child{
margin-bottom: 0;
}

.page{
min-height: 100vh;
display: flex;
flex-direction: column;
justify-content: space-around;
}

.page__demo{
flex-grow: 1;
}

.main-container{
max-width: 960px;
padding-left: 2rem;
padding-right: 2rem;

margin-left: auto;
margin-right: auto;
}

.page__container{
padding-top: 30px;
padding-bottom: 30px;
max-width: 800px;
}

.footer{
padding-top: 1rem;
padding-bottom: 1rem;
text-align: center;
font-size: 1.4rem;
}

.footer__link{
text-decoration: none;
color: inherit;
}

@media screen and (min-width: 361px){

.footer__container{
display: flex;
justify-content: space-between;
}
}

@media screen and (max-width: 360px){

.melnik909{
display: none;
}
}

Hi there,

this CSS is causing the issue:

.page {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: space-around;
}

.page__demo {
    flex-grow: 1;
}

I can't see it is required and can be removed.

Great, thanks.

You're welcome