Use bootstrap 4 in the main page

customize.dist/src/less/variables.less

@@ -55,7 +55,11 @@
 @topbar-color: #000;
 @topbar-button-bg: #2E9AFE;
 @topbar-button-color: #fff;
+@topbar-height: 50px;
 
 @main-border-width: 15vw;
 @cp-darkblue: #3333ff;
 @cp-accent2: darken(@cp-darkblue, 20%);
+
+@main-block-bg: rgba(200, 200, 200, 0.3);
+@main-color: #fff;