Aslında çok şey var ama buradan başlayarak.
Biraz daha düzenleme ile devam edebilirsiniz.
Özellikle, logonuzu öncelikli olarak revize edip. Sloganınızın logonun altına almanızı öneririm.

@import url('https://fonts.googleapis.com/css2?family=Poppins:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,100;1,200;1,300;1,400;1,500;1,600;1,700;1,800;1,900&display=swap');
body {
font-family: "Poppins", sans-serif !important;
}
.header {
padding-top: .75rem;
padding-bottom: .75rem;
background: linear-gradient(to left, #6fbdf5, #45aaf2);
border-bottom: 1px solid #d7e7ff;
}
.Klast-navbar .nav-link {
font-size: 15px;
}
.Klast-navbar .nav-link.active {
color: #45aaf2;
}
.Klast-navbar .nav-link {
color: #56585c;
}
.header .btn-success {
background: #1a84d0;
line-height: 0 !important;
border-radius: 6px;
display: flex;
justify-content: center;
align-items: center;
height: 44px;
border-color: #1a84d0;
box-shadow: 0 3px 27px rgba(0, 0, 0, 0.07);
}
.header .btn-info {
line-height: 0 !important;
border-radius: 6px;
display: flex;
justify-content: center;
align-items: center;
height: 44px;
background-color: #063d64;
border-color: #063d64;
box-shadow: 0 3px 27px rgba(0, 0, 0, 0.07);
}
.header .order-lg-2 {
align-items: center;
}
.carousel-caption .btn-red {
color: #fff;
background-color: #49acf2;
font-size: 16px;
font-weight: 600;
border-radius: 6px;
border-color: #49acf2;
}
.carousel-inner {
box-shadow: 0 3px 27px rgba(0, 0, 0, 0.07);
}
.card-aside-column {
min-width: 5rem;
width: 40%;
-ms-flex: 0 0 40%;
flex: 0 0 40%;
}
.card-aside .card-body h4 a {
color: #2799d8;
}
.btn-orange {
border-color: #2799d8;
background: #2799d8;
color: #fff;
}
.card-aside .card-body .text-muted {
color: #646464 !important;
}
a {
color: #55555c;
}