Make buttons all the same width and remove some css

This commit does the following things:
- remove some unused css code
- Make buttons the same with on the startpage (solves #24)

frontend/src/components/HeroSection.css

@@ -1,11 +1,3 @@
-video {
-  object-fit: cover;
-  width: 100%;
-  height: 100%;
-  position: fixed;
-  z-index: -1;
-}
-
 .hero-container {
   background: url("../images/fingerprint_biometrics.jpg") center center/cover
     no-repeat;
@@ -42,6 +34,7 @@ video {
 
 .hero-btns .btn {
   margin: 6px;
+  width: 100%;
   align-items: center;
 }
 
@@ -51,10 +44,6 @@ video {
   border: none;
 }
 
-.fa-play-circle {
-  margin-left: 4px;
-}
-
 @media screen and (max-width: 960px) {
   .hero-container > h1 {
     font-size: 70px;