Hello, I need help \:D/

Hello, I'm a new customer of GeneratePress, I have just bought your premium package.

Because I wanted to implement my own design idea, I added some CSS, it seems like it worked but didn't match well. Can you help me fix it?

Because I'm not very specialized in this area, I would like to have a final result on these CSSs to add.

Here are all the CSS that I have added:

/* Tao hieu ung Link underlines */
.entry-content a:not(.button) {
box-shadow: inset 0 -1px 0 currentColor;
transition: color 100ms ease-in,box-shadow .13s ease-in-out;
}
.entry-content a:not(.button):focus, .entry-content a:not(.button):hover {
box-shadow: inset 0 0 0 currentColor,0 3px 0 currentColor;
}

/* Tao hieu ung Hover Effect cho Menu */
.main-navigation .menu>.menu-item>a:before,
.main-navigation .menu>.current-menu-item:not(.wc-menu-item)>a:before,
.loud-link a:before {
    content: "";
    position: absolute;
    display: block;
    bottom: -0em;
    width: 0%;
    height: 3px;
    background-color: currentColor;
    -webkit-transition: 0.2s width ease;
    transition: 0.2s width ease;
}

.main-navigation .menu>.menu-item>a:hover:before,
.main-navigation .menu>.current-menu-item:not(.wc-menu-item)>a:before,
.loud-link a:hover:before {
    width: calc(100% - 30px);
}

/* Tao hieu ung bong do cho Static-Navigation */
#site-navigation {
	box-shadow: 0 2px 4px -1px rgba(0,0,0,0.25);
}

/* Tao hieu ung bong do cho Sticky-Navigation */
nav#sticky-navigation {
	box-shadow: 0 2px 4px -1px rgba(0,0,0,0.25);
}

/* Tao hieu ung bo tron */
.inside-article, .comments-area, .widget, .page-header, .button {
    border-radius: 5px;
}

/* Tao hieu ung bong do (drop shadow) */
.inside-article, .comments-area, .widget, .page-header {
    box-shadow: 0 2px 4px -1px rgba(0,0,0,0.25);
}

/* Chinh Page-Header */
.page-header {
background: rgb(255,255,255);
background: radial-gradient(circle, rgba(255,255,255,1) 50%, rgba(217,248,255,1) 100%);
}

/* Chinh giao dien mobile */
@media (max-width: 768px) {
    .container {
        margin-left: 8px;
        margin-right: 8px;
    }
}

Thank you \:D/